
Copyright!! - 



COPYRIGHT DEPOSIT. 



I 



THE 

SOURCES AND MODES 

OF 

INFECTION 



By 
CHARLES V. CHAPIN, M.D., Sc. D. 

SUPERINTENDENT OF HEALTH, PROVIDENCE, R. I. 
AUTHOR OF "MUNICIPAL SANITATION IN THE UNITED STATES" 



FIRST EDITION 

FIRST THOUSAND 



NEW YORK 
JOHN WILEY & SONS 

London: CHAPMAN & HALL, Limited 
1910 



f ¥ V • • • 



Copyright, 1910, 
By CHARLES V. CHAPLN 



Stanbopc lpres& 

f, H. GILSOH COUPAH" 
BOSTON. U.S.A. 



CI.A268935 



PREFACE. 



This volume is intended to indicate the principles which 
should guide sanitary practice, and to show how recent labo- 
ratory work and the epidemiological study of disease have 
modified these principles. When I began work as health offi- 
cer in 1884 the filth theory was still in favor, and it was 
generally believed that the germs of disease commonly grew 
in decaying organic matter. Yet contagion was recognized 
as an important factor in the spread of disease, and the isola- 
tion of the sick was more and more insisted upon. Fifteen 
years ago probably most health officials believed that the 
contagious diseases could be completely stamped out if only 
all persons sick with them could be isolated. The air was 
thought to be the chief medium for their transmission, and 
fomites the mechanism for their passage from place to place. 
Sanitary practice was based on these premises. 

My own views concerning these matters became greatly 
modified year by year, partly owing to the rapidly accumu- 
lating knowledge of bacteria and other disease-producing 
organisms, and partly owing to direct observations on the 
manner in which the infectious diseases are disseminated, and 
on the effect of preventive measures. 

It now appears that the growth of disease germs outside of 
the body is not frequent enough to be an important factor in 
the causation of disease, but their growth in the body with- 
out causing sickness, their latency as it were, often for many 
months, is a factor of very great significance. We know now 
that direct contact with the sick, or with healthy carriers of 
disease germs, is an exceedingly frequent mode of transmis- 
sion, and that infection by means of the air, or from infected 
articles, is not nearly as common as was formerly believed. 

iii 



IV PREFACE 

We are now better able than ever before to attribute to water 
and milk their proper share in the distribution of infection. 
The recent discovery of the transmission of disease by insects 
gives us entirely new and most effective means of combating 
disease. It is time that sanitary measures directed against 
the infectious diseases should be modified to correspond with 
existing knowledge. Present-day theories and present-day 
practice are maintained largely by tradition, and to facilitate 
the adaptation of practice to the facts as we now know them, 
is the purpose of this book. Some modifications of sanitary 
practice are suggested, but no attempt is made to discuss 
details; rather are general principles presented, which it is 
believed ought to guide administrators in their work. 

While some of the following pages may seem rather radical 
to many, I believe that practically all laboratory workers will 
agree with the contents of the first chapter, and that a large 
number of bacteriologists and health officers are convinced of 
the great importance of " carriers " and mild unrecognized 
cases. The tendency among many, too, is to lay less emphasis 
on infection by fomites, though perhaps few are ready to 
give up routine terminal disinfection for the common infec- 
tious diseases. So also there are very many careful observers 
who are attributing more and more importance to what is 
generally called contact infection. 

The public health administrator is placed at great disad- 
vantage because he is obliged to base his acts on knowledge 
which is far from exact. The laboratory workers have accu- 
mulated a vast mass of quite exact data in regard to the caus- 
ative relation of bacteria and protozoa to disease, and no one 
appreciates this more than the writer, but there are many 
problems which the laboratory men cannot solve, and many 
others which they have failed to solve. The epidemiologist 
must study in the field the way in which disease is caused. 
He must use the statistical method, and the application of 
statistical methods to epidemiology is more difficult and less 
attractive than laboratory experiment. 



PREFACE V 

We need to measure more carefully the relative importance 
of different sources of disease and different modes of infec- 
tion. It is not so important to know that typhoid bacilli 
live in water for weeks, as it is to know that 99 per cent die 
in one week. It is not enough to discover that diphtheria 
bacilli can be recovered from articles in the sick-room; we 
must learn how often they are found and how often disease 
is traced to such a source. We have for years been much 
alarmed because tubercle bacilli are found in milk, but since 
a serious effort has been made to measure the actual danger, 
the alarm has greatly diminished. Doubtless the house fly 
has been the cause of typhoid fever, but in what percentage 
of cases we are profoundly ignorant. Healthy carriers of 
diphtheria have certainly transmitted the disease to others, 
and we should earnestly try to determine the amount of 
diphtheria caused in this way. The attempt is made in the 
following pages to estimate roughly, with the very imperfect 
material now available, the relative importance of different 
factors in the extension of infectious diseases. The conclu- 
sions must to a large extent be merely tentative, and as 
indicating lines for further study. 

I am under great obligations to my friends Dr. H. W. Hill 
and particularly Prof. F. P. Gorham for many suggestions 
and criticisms, but neither is to be considered at all 
responsible for any of the views presented. 

The book is intended primarily for health officers and phy- 
sicians, but it is hoped that many others will find some parts 
interesting and suggestive. 

CHARLES V. CHAPIN. 

Providence, April, 1910. 



CONTENTS. 



CHAPTER I. 

LIFE OF DISEASE GERMS OUTSIDE OF THE BODY. 

Review of evidence of growth of disease germs outside the body, 
anthrax, black leg, tetanus. — Typhoid bacilli in soil, water, ice, 
milk. — Epidemiological evidence relating to typhoid fever. — Evi- 
dence relating to cholera, Mediterranean fever, plague, dysentery, 
bacteria of suppuration, diphtheria and various other diseases. — 
Reasons for former belief in "filth theory" of disease. — Epidemio- 
logical evidence against soil infection. — Conclusions. — Relations of 
these views to public sanitation. 

CHAPTER II. 

CARRIERS AND MISSED CASES. 

Importance of the subject. — Evidence of the occurrence of carriers 
and missed cases, and reference to disease caused by them in typhoid 
fever, cholera, dysentery, cerebro-spinal meningitis, diphtheria, glan- 
ders, influenza, pneumonia, gonorrhea, tuberculosis, leprosy, suppura- 
tion, tetanus, scarlet fever, smallpox, measles, protozoan diseases, such 
as cattle fever, malaria, sleeping sickness, nagana, syphilis, amebic 
dysentery and yellow fever. — Conclusions. 

CHAPTER III. 

LIMITATIONS TO THE VALUE OF ISOLATION. 

The number of carriers and missed cases. — Not realized by health 
officials. — Failure of isolation in Providence. — Hospitalization has 
not materially lessened infectious disease. — Less isolation followed by 
less diphtheria in Providence. — Failure of isolation in institutions. — 
Failures in the isolation of measles, of cerebro-spinal meningitis, of 
smallpox. — Failure due to carriers and missed cases. — Difficulties in 
the isolation of diphtheria. — Absolute isolation not possible. — Mod- 
erate isolation sufficient. — Infection not so easy as was believed. — 
Isolation effective at the beginning of an outbreak, rarely later. — The 
more carriers the less effective is isolation. — True value of isolation 
hospitals. — Details of home isolation. — Summary. 



VU1 CONTENTS 

CHAPTER IV. 

INFECTION BY CONTACT. 

Transmission of gonorrhea by indirect contact. — Of syphilis in the 
same way. — Typhoid fever spread by contact. — Reasons why contact 
infection has been disregarded. — Mode of contact infection in typhoid 
fever. — Contact infection in dysentery. — Cholera. — Ankylostomi- 
asis. — Gonorrhea. — Transfer of nasal and oral secretions by contact. 
— Presence of germs in secretions and on various objects. — Diseases do 
not spread from family to family in tenements. — No cross infection 
in hospitals except by contact. — Contact infection in tuberculosis. — 
Protection from contact infection a personal matter. — Need for urging 
personal cleanliness. 

CHAPTER V. 

INFECTION BY FOMITES. 

Definition. — Fomites and yellow fever. — Examples of alleged 
fomites infection. — Infection by clothing, rooms, rags, money. — Fomites 
infection in tetanus, anthrax, typhoid fever, diphtheria, plague. — No 
evidence that fomites are of much importance. — Reasons for belief in 
fomites. — Effect of drying on bacteria of different kinds. — The find- 
ing of bacteria on fomites. — Drying of vaccine and smallpox virus. — 
Summary of bacteriological evidence. — Experimental work with yellow 
fever, plague. — Results of abandoning disinfection in Providence. — 
Disinfection in other diseases. — Conclusions. 

CHAPTER VI. 

INFECTION BY AIR. 

Alleged aerial transmission of smallpox, scarlet fever, diphtheria, 
typhoid fever, influenza, measles. — History of surgical technique shows 
that air-borne infection is of little moment. — Air-borne anthrax. — 
Bacteria not given off from moist surfaces. — Bacteria carried in dust. — 
Dust and the germs of typhoid fever, diphtheria, plague. — Dust and 
tubercle bacilli. — Finding of tubercle bacilli in dust. — Other bacteria 
in dust. — Droplet infection. — Finding of bacteria in air. — Experi- 
mental work with tuberculosis, Mediterranean fever, anthrax, plague. — 
Conclusions. 

CHAPTER VII. 

INFECTION BY FOOD AND DRINK. 

The Broad Street well. — North Boston well. — Typhoid fever due 
to water. — Cholera, dysentery, diarrhea, malaria and yellow fever. — 
Purification of water. — Ice. — Milk, number of outbreaks. — Mode 



- CONTENTS ix 

of infection of the milk. — Tuberculosis and milk, evidence of infec- 
tion. — Bacilli in market milk. — Amount of tuberculosis due to milk. 

— Mediterranean fever, anthrax, foot-and-mouth disease, rabies. — 
Diarrhea. — Infection by meat. — Infection by shellfish. — Crawfish. 

— Watercress. — Celery. 

CHAPTER VIII. 

INFECTION BY INSECTS. 

Insects as biological and as mechanical carriers. — Pioneer work of 
Smith and Kilborne in cattle fever. — Malaria. — Modes of control : quinia, 
isolation, screening; mosquito reduction; practical results. — Yellow 
fever carried by mosquitoes, not by fomites. — Control of yellow 
fever; quarantine, isolation; mosquito control; practical results. — 
Filariasis, sleeping sickness, kala-azar, dengue, relapsing fever, Rocky 
Mountain fever. — Bubonic plague and fleas. — Anthrax. — Carriage 
of bacteria on the bodies of insects. — Flies as carriers of disease, of 
cholera, dysentery and diarrhea. — Typhoid fever, prevailing views 
as to relation of flies to disease. — Statistical proof. — Control of fly 
nuisance. — Conclusions. 



THE SOURCES AND MODES OF 
INFECTION. 



CHAPTER I. 

LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 

Former Theories. — From time immemorial miasms, ma- 
larias, vapors and emanations, gaseous or otherwise, have 
been believed to be the frequent cause of disease. These 
miasms were thought to arise from stagnant marshes, decay- 
ing vegetation, putrid animal matter, and indeed filth 
of every kind. This belief in the extra-corporal origin of 
disease reached its widest acceptance about the middle of 
the nineteenth century. The rise of the germ theory greatly 
strengthened it. The discovery of bacteria and of their 
wide distribution and almost universal growth in dead 
organic substances, and the theory that these bacteria were 
the real cause of disease, led men to look for the source of 
disease outside of the body, and chiefly in dead animal and 
vegetable matter. With the passing of the germ theory as 
a theory, and with the demonstration of the parasitic nature 
of so many of our most important and dreaded diseases, the 
opportunity was afforded for studying in detail the bacteria 
and protozoa which are the specific causes of these diseases. 
Much has been done by laboratory workers to unravel the 
life history of these minute forms, and it is well for us to 
examine the knowledge thus gained, and also the newer 
epidemiological observations on the spread of the infectious 
diseases, and in the light of these data question the belief 
that these diseases have their origin in the outer world rather 

1 



2 THE SOURCES AND MODES OF INFECTION 

than in the bodies of men or animals. Let us consider some 
of these diseases in detail. 

Anthrax is not common in the United States, but it is of 
much interest from a scientific standpoint. It was the first 
disease definitely proved to be caused by bacteria. It is 
of particular interest in this connection because a relation 
to the soil has been better established for this than for any 
other disease. Practically all writers are agreed that the 
soil may become infected with anthrax, and remain so for 
a long time, and that animals pastured upon such soil con- 
tract the disease by taking the bacteria in with the food, 
or inspired air, or through abrasions of the skin. That this 
soil infection is not the sole, or perhaps even the most com- 
mon source of infection, and that danger from this source 
has perhaps been somewhat exaggerated, is probably true. 
Thus Delepine L from studying recent outbreaks in Great 
Britain is convinced that the disease is perpetuated by 
a more or less direct contact, chiefly with unrecognized or 
concealed cases, and that there is no necessity for supposing 
a long continued soil infection, and no direct evidence for 
it as the principal source of the disease. McFadyean 2 can- 
not trace anthrax in Britain to the soil, and thinks it im- 
probable that it grows there, or it would be more common. 
Moreover it does not grow well under 60°. Legge 3 notes that 
animal anthrax does not increase in the summer as it would 
be likely to if it were due to growth in the soil. Moore 4 does 
not think the bacillus maintains a saprophytic existence. 
In Louisiana 5 the extensive outbreak in the latter years of 
the nineteenth century was believed to be due to some extent 
to food infection, and to a large extent to direct inoculation 

1 Delepine, Pub. Health, 1904-5, XVII, 491. 

2 McFadyean, J. Comp. Path, and Therap., Edinb. and Lond., 1903, 
XVI, 35. 

3 Legge, Lancet, Lond., 1905, I, 695. 

4 Rep. Comm. of Agric. N. Y., 1907. 

5 Louisiana Agricultural Experiment Sta., Bull. No. 60, 2d. s., 1900. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 3 

by a species of horsefly, Tabanus lineola. Outbreaks of 
anthrax have occurred every few years in Louisiana for over 
half a century, and persistent soil infection has been alleged 
as their source. Very likely it is so to a certain extent, but 
on the other hand there is no doubt that the interval be- 
tween the outbreaks may well be bridged over by a more or 
less direct connection between sporadic and unrecognized 
cases occurring in the interval. That such cases really occur 
is shown by Delepine's investigations of similar conditions 
in England. Nevertheless almost all veterinary and medical 
writers are agreed as to the long continued soil infection of 
certain areas. Evidence of this is forthcoming from France, 
Germany, England 1 and the United States. In England such 
infective areas are said to be the most numerous where refuse 
from mills using foreign wools is used for manure. In this 
country anthrax is believed to have been traced to morocco 
factories on the Delaware River using large numbers of 
foreign skins. 2 Some of the infected Delaware farms had new 
tenants with new cattle each year, but infection recurred. 
All the evidence pointed to persistent infection of the soil. 
Similarly infected farms or fields are reported from New Jer- 
sey, 3 from the Genesee valley 4 and from Louisiana. 5 Law 
reports that 200 cases in cattle, and 3 in human beings re- 
sulted in the space of two weeks, from the soil infection of a 
limited area. Dr. Leonard Pearson wrote me that the evi- 
dence is conclusive that soil infection with anthrax has existed 
in a number of places in Pennsylvania. Two instances have 
recently been reported which seem to show pretty conclu- 
sively that anthrax bacilli do grow in small ponds under 

1 Poore, The Earth in Relation to the Preservation and Destruction 
of Contagia, Lond., 1902, 9-21. 

2 Delaware Agricultural Experiment Sta., Bull. No. 32, 1896, 6. 

3 Rep. St. Bd. Health, N. J., 1904, 5. 

4 Law, Text-Book of Veterinary Medicine, Ithaca, 1902, IV, 195. 

5 Louisiana Agricultural Experiment Sta., Bull. No. GO, 2d s., Insert 
opp. 345, and 357. 



4 THE SOURCES AND MODES OF INFECTION 

natural conditions. Dr. J. Sinclair Holden, health officer of 
Sudbury, Co. Suffolk, England, writes that in 1905 the waste 
water from a horsehair factory was discharged into a small 
pond. There was evidently some seepage from this pond to 
another about 20 feet distant. The second pond, in the fol- 
lowing year, was found to be so abundantly filled with the 
bacilli of anthrax that it seemed that there must have been 
free reproduction. Hastings x also reports that he examined 
a pond which had received anthrax-infected tannery refuse, 
and that this was teeming with the vegetative forms of the 
bacillus. 

While there is a good deal of 'evidence, apparently conclu- 
sive, that soil may remain infected with anthrax for years, 
there also is evidence that the infection after a time disap- 
pears. Pasteur records instances of the infection dying out 
after a lapse of some years, 2 and in Delaware infection did 
not persist on all the infected farms. 3 The fact that anthrax 
has appeared at so many isolated points in England and the 
United States, and though in the majority of cases soil inocu- 
lation must have taken place, nevertheless the fact that the 
disease has never become widespread or long persistent locally 
is sufficient reason for the conclusion that its virus does not, 
in these countries at least, find a suitable soil. If it increases 
at all in the soil it is only for a time, and the tendency is for 
it to die out. In other words, the history of this disease is 
best explained on the hypothesis that the soil is infected 
chiefly if not exclusively by the spores, which may retain 
their virulence for years, but which rarely germinate in the 
earth. 

Charbon Symptomatique. — Another animal disease known 
as black-leg, or in Europe as charbon symptomatique, is 

1 Hastings, Paper read at meeting of Society of American Bacteri- 
ologists, 1908. 

a Poore, The Earth in Relation to the Preservation and Destruction 
of Contagia, Lond., 1902, 13. 

3 Delaware Agricultural Experiment Sta., Bull. No. 32, 1896, 7. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 5 

quite prevalent among cattle in this country. Like anthrax 
it is caused by a bacillus that forms spores. Veterinarians 
are agreed that soil areas become infected with black-leg and 
may remain so for some time. Undoubtedly this infection 
may be explained, as is the infection by anthrax, as due simply 
to the resistance of the spores, and does not necessarily re- 
quire the actual multiplication of the germs in the soil. 

Tetanus or lockjaw, even before it was known to be due 
to a bacillus, was believed to occur with exceptional fre- 
quency in limited areas. It has been stated by numerous 
writers that there is a strip of land near Red Bank, New 
Jersey, where tetanus is decidedly endemic. The disease was 
also said to be formerly extremely common, especially 
among animals, on the eastern end of Long Island, but that 
it has now become quite rare in that locality. This alleged 
local prevalence on Long Island has been, in this country at 
least, one of the most frequently used arguments in sup- 
port of soil infection, but Overton 1 has shown that the 
published statements cannot be verified, and that the disease 
has not been especially prevalent in that locality. I have 
corresponded with various officials in New Jersey, but have 
never been able to obtain any evidence of the alleged local 
infection at Red Bank. Tetanus is more common in the 
southern than in the northern parts of the United States, 
and is a very important cause of death in the West Indies. 
Before the organization of the present efficient health depart- 
ment in Havana there were often 200 deaths or more annually 
from infantile tetanus, due to infection of the navel. It has 
long been recognized that tetanus follows wounds in which 
dirt is forced deep into the tissues, and that garden earth is 
especially dangerous. Even well-established evidence of per- 
sistent local infection does not prove growth in the soil. It 
might be due to a great variety of causes. 

Thus it has been explained that the bacilli of tetanus are 
very widely distributed because these bacteria are natural 

1 Overton, Long Island M. J., Brooklyn, 1907, I, 176. 



6 THE SOURCES AND MODES OF INFECTION 

inhabitants of the healthy intestines of domestic animals, 
particularly the horse. Hence they are found in profusion 
wherever the manure from these animals falls, and soiled skin 
and clothing are not likely to carry them. Theobold Smith, 1 
however, says that there is no evidence that the tetanus 
bacilli are normal inhabitants of and multiply in the intes- 
tines of animals. He inclines to the view that their home is 
in the soil. Vincent 2 after introducing tetanus spores into 
the stomach of a rabbit could find no evidence of multipli- 
cation, and he, too, thinks a saprophytic existence probable. 
The tetanus bacillus forms spores which may retain their 
vitality for 16 years, so that it is not surprising that lands 
have been known to remain infected for several years. 3 These 
spores, or the bacilli, are said to have been found in gelatine, 4 
in blank cartridges, 5 and on balls of lamp wick used in Havana 
for tying the umbilical cord. 6 While the soil, and dirt gener- 
ally, contain tetanus bacilli or their spores, there is no direct 
evidence to show that they are propagated outside of the body. 
The fact that they do not grow in the presence of air would 
indicate that this is not the case, and the distribution of the 
disease and its comparative rarity would also lead to this 
conclusion. It is not, of course, to be denied that the tetanus 
bacillus may lead a saprophytic existence. It is very pos- 
sible that it may do so, but it certainly can be affirmed that 
at present we have no proof that it does so, and all observed 
facts relating to the bacillus, or the disease caused by it, may 
be explained without assuming any such hypothesis. 

It is suggestive that the pathogenic bacteria which are 
oftenest assumed to grow in the soil are the very ones the 

1 Theobold Smith, J. Am. Ass., Chicago, 1908, L, 929. 

2 Vincent, Compt. rend. Soc. de biol. Par., 1908, LXV, 12. 

» Villar, J. Comp. Path, and Therap., Edinb. and Lond., 1897, XX. 
4 Tuck, J. Path, and BacterioL Edinb. and Lond., 1904, IX, 38. 
1 Dolley, J. Am. M. Ass., Chicago, 1905, XLIV, 466. 
6 Junta Superior de Sanidad de la Isla de Cuba, Suplemento y Noto 
idicional, 1902-3, 4.^ 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 7 

spores of which may retain their vitality for years. Is it not 
more likely that it is persistence of spores, rather than growth 
of the bacilli themselves, that in most instances maintains 
the soil infection ? 

Typhoid Bacilli in Soil. — It has been amply demonstrated 
that water, milk, soil and various other materials are, when 
sterile, suitable media for the growth of the typhoid bacillus. 
But this fact is of little practical importance, as sterile mate- 
rials are not ordinarily found in nature, but on the contrary 
almost everything which could possibly be considered a cul- 
ture medium for typhoid and other disease germs is swarming 
with bacteria, mostly of entirely harmless varieties. There 
has been much painstaking work to determine whether ty- 
phoid bacilli actually do grow, or even retain their vitality, 
in or on a great variety of substances. The difficulties in 
this sort of experimentation are considerable, and not the 
least is that of picking out the typhoid bacillus from among 
other forms. Robertson 1 and Firth and Horrocks 2 seem to 
have made the most elaborate experiments in regard to its 
growth in soil, and to have worked under more natural con- 
ditions than most observers. Robertson found that by 
moistening soil from time to time with bouillon he could 
keep the bacillus alive for 11 months, and even cause it to 
grow. Firth and Horrocks did not find any evidence of 
increase in soil under a great variety of conditions. When 
conditions were favorable it could be recovered up to 74 days. 
In peat it could only be recovered after 13 days. More 
recently Mair 3 has been able to recover the bacillus from un- 
sterilized soil in large numbers, for 20 days, and in small 
numbers, up to 70 or 80 days. He found no evidence of 
increase. Great care was taken not to introduce any nutri- 
tive medium with the bacilli. Unlike most observers, Mair 
found that in sterile soil the bacilli disappear more rapidly, 

1 Robertson, Brit. M. J., Lond., 1898, I, 69. 

2 Firth and Horrocks, Brit. M. J., Lond., 1902, II, 936. 

3 Mair, J. Hyg., Cambridge, 1908, VIII, 37. 



8 THE SOURCES AND MODES OF INFECTION 

in 11 days in fact. He believes that this is due to the chem- 
ical composition of the particular soil used. Smith l working 
with similar soil, unsterilized, could not recover the organism 
after 25 days, and the average duration in the soil was 15 
days. Most observers, as Koch, 2 Karlinski, 3 Uffelmann, 4 
Martin, 5 Pfuhl 6 and others agree that it does not grow in soil, 
though it may retain its vitality at times for months. Savage 7 
found that it died rapidly in tidal mud, though a few bacilli 
could be recovered after five weeks. Klein 8 could not find 
the organism in dead animals buried in earth, after 20 days, 
but Loesner 9 found it after 96 days. 

Typhoid Bacilli in Sewage. — According to Park 10 typhoid 
bacilli soon die out in feces, usually in a few hours, but he 
has recovered them up to the tenth day. He suggested that 
this variation may depend on the constitution of the feces. 
On the other hand, Levy and Kayser 11 note the persistence of 
typhoid bacilli in a cemented privy vault up to 5 months 
and Pfuhl 6 recovered them after 3 months from feces mixed 
with garden earth. Delepine 12 states that typhoid bacilli will 
survive in a privy for a year. Rogers 13 found that the bacillus 
lived only a few days in filtered septic tank effluent. 

1 Smith, Rep. on Occurrence of Typhoid Fever in Belfast, 1903, 
quoted by Mair. 

2 Koch, Die Bek mpfung des Typhus, Berl., 1903, 14. 

3 Karlinski, Arch. f. Hyg., Miinchen u. Leipz., 1891, XIII, 302. 
* Uffelmann, Centralbl. f. Bakteriol. [etc.1, Jena, 1894, XV, 133. 

5 Martin, Rep. Med. Off. Local Gov. Bd., Lond., 1900-1901, XXX, 
508. 

6 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 

7 Savage, J. Hyg., Cambridge, 1905, V, 146. 

8 Klein, Rep. Med. Off. Local Gov. Bd., Lond., 1898-9, XXVIII, 363. 

9 Loesner, Arb. a. d. k. Gsndhtsamte, Berl., 1896, XII, 448. 

10 Park, J. Am. M. Ass., Chicago, 1907, XLIX, 852. 

11 Levy and Kayser, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 
1902, XXXIII, 489. 

12 Delepine, Rep. Health of Manchester, 1907, 82. 

13 Rogers, Brit. M. J., Lond., 1903, II, 639, 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 9 

Typhoid Bacilli in Water. — Hoffmann 1 could recover ty- 
phoid germs from aquarium water after 36 days, or from mud 
after 2 months. Jordan and Russell 2 tried to imitate natural 
conditions by enclosing inoculated water in colloidal sacs to 
permit of osmosis, and these were placed in the Chicago 
River, a sewage-polluted stream. They could recover the 
bacilli for from 3 to 7 days only. Russell and Fuller 3 repeated 
these experiments with substantially the same results, though 
they kept the bacillus alive in lake water from 8 to 10 days. 
Karlinski 4 could not recover typhoid bacilli from water after 
6 days, except once in cistern water, where they persisted for 
13 days. Hewlett 5 never found them alive in sterilized Lon- 
don tap water over 4 weeks. Houston 6 has recently made 
some careful quantitative studies of the life of the typhoid 
bacillus in raw London tap water. In eighteen series of tests 
the average reduction during the first week was 99.9 percent, 
but a few could be recovered up to the eighth week. 

Field 7 found that typhoid bacilli would survive in sea 
water for from 6 to 8 days, but that 50 percent died in 24 
hours. 

Wheeler 8 finds that in well water with considerable pollu- 
tion, at room temperature, and with the exclusion of light, 
a considerable increase of typhoid organisms may take place. 
Konradi 9 also claims that this bacillus can maintain a sapro- 
phytic existence in water, but his methods have been criti- 
cized, and in some experiments at least, a good deal of nutrient 

1 Hoffmann, Arch. f. Hyg., Miinchen u. Leipz., 1905, LII, 208. 

2 Jordan and Russell, J. Infect. Dis., Chicago, 1904, I, 641. 

3 Russell and Fuller, J. Infect, Dis., Chicago, 1906 [Suppl. No. 2], 40. 

4 Karlinski, Centralbl. f. Bakteriol. [etc.], Jena, 1889, VI, 138. 

5 Hewlett, J. State M., Lond., 1905, XIII, 165. 

^ 6 First Rep. on Research Work Metrop. Water Bd., Lond., Abst. 
Pub. Health Lond., 1908, XXII, 30. 

7 Field, Rep. Dept. Health, City of New York, 1904, 1, 451. 

8 Wheeler, J. Med. Research, Bost., 1906, XV, 269. 

9 Konradi, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1904, 
XXXVI, 203J 



10 THE SOURCES AND MODES OF INFECTION 

material was added to the water with the organisms. The 
report on typhoid fever in the District of Columbia 1 quotes 
from Kubler and Neufeld, and Stroezner and Tavel, instances 
of alleged longevity of the typhoid bacillus in well water or, 
in Tavel's case, in tap water, but secondary contact infec- 
tion was not in any instance absolutely excluded. On the 
other hand, the infection in a reservoir in Scranton was 
proved to have died out within 8 weeks. 2 

Pf uhl 3 found the bacillus in tap water after 28 days, but not 
after 31 days. In artificially inoculated seltzer water it lived 
for 27 days. Hill, 4 however, could not recover it from various 
carbonated " soft drinks " after 14 hours. 

Typhoid Bacilli in Ice. — Various writers have studied the 
life of typhoid bacilli in ice, and Prudden, 5 Winslow, 6 Park, 7 
Jordan, Russell and Zeit, 8 Clark, 9 Smith and Swingle 10 and 
Wheeler 11 have shown that they tend to disappear gradually, 
somewhat as they do in the water from which the ice is 
obtained. Yet an outbreak is recorded caused by typhoid 
bacilli frozen in ice for eight months. But they were in con- 
siderable masses of feces. 12 This is the only reported outbreak 
in which it is reasonably certain that infection was by ice. 

Typhoid and Oysters. — Field 13 found that in healthy 
oysters typhoid germs rapidly died, and none could be re- 
covered after the ninth day. When the oysters were dead 

1 U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 35, 178. 

2 N. York M. J. [etc.], 1907, LXXXV, 1025. 

8 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 

4 Hill, Rep. Bd. of Health, Bost., 1904, 53. 

6 Prudden, Med. Rec., N. Y., 1887, XXXI, 341. 

6 Winslow, J. Mass. Ass. of Bds. Health, Bost., XI, 133. 

7 Park, J. Bost. Soc. M. Sc., 1899-1900, IV, 213. 

8 Russell and Zeit, J. Infect. Dis., Chicago, 1904, I, 660. 

9 Clark, J. Mass. Ass. Bds. Health, Bost., XI, 124. 

10 Smith and Swingle, Science, N. Y., 1905, n. s., XXI, 481. 

11 Wheeler, J. Med. Research, Bost., 1906, XV, 269. 

12 Am. J. M. Sc, Phila., 1903, n. s., CXXVI, 680. 

13 Field, Med. News, N. Y., 1904, LXXXV, 571. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 11 

or dying, there was a very considerable increase. Klein x 
found that in oysters kept in sea water typhoid bacilli would 
live from 6 to 7 days, but if kept out of the water, for 11 days. 
In other shellfish their life was longer. 

Typhoid and Milk. — Sterile milk serves as an excellent 
culture medium for the typhoid bacillus, but ordinary market 
milk is not favorable for its growth, owing to the rapid pro- 
duction of lactic acid. Bassenge 2 says that when milk has 
soured to the extent of 0.3°-0.4° Soxhlet, and has continued 
in this condition for 24 hours, the bacilli are destroyed. Neu- 
feld 3 states that they usually disappear from ordinary milk 
in from 2 to 3 days. Pfuhl 4 found the bacillus persisting in 
the milk for 13 days. Rosenau and McCoy have studied 
this question and reviewed the literature. 5 They find that 
raw milk, when first drawn, has a feeble antiseptic action, 
and typhoid and dysentery bacilli, when added to it, decrease 
slightly at times, but within 48 hours their numbers increase 
enormously. Eyre 6 also states that the typhoid bacillus 
may increase in milk to enormous numbers, but as the 
milk he experimented with was drawn under careful aseptic 
precautions, it is quite likely that his findings would not 
obtain in ordinary milk, owing to the hostile influence of 
lactic-acid and other bacteria. 

If typhoid bacilli increase in number in ordinary market 
milk, extensive outbreaks ought to be expected in our large 
American cities, where the milk is handled by large dealers 
drawing their supply from many producers situated at long 
distances, so that the milk is from 48 to 72 hours old before 

1 Klein, Tr. Path. Soc. Lond., 1905, LVI, 23; Med. Press & Circ, 
1905, LXXIX, 264. 

2 Bassenge, Deutsche med. Wchnschr., 1903, XXIX, 675, 697. 

8 Neufeld, Kolle u. Wassermann, Handbuch [etc.] Jena, 1903, II, 213. 

4 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 

5 U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 41, 
449. 

6 Eyre, J. State M. Lond., i904, XII, 728. 



12 THE SOURCES AND MODES OF INFECTION 

it reaches the consumer. Any dilution ought to be more 
than balanced by the alleged increase in the bacteria. But 
nearly all of the American milk outbreaks reported in 
Bulletin 41 of the Hygienic Laboratory were on small 
routes where the interval between infection and delivery was 
short. No outbreaks due to railroad milk were reported 
from Boston, New York, Philadelphia, Chicago, Buffalo, 
Baltimore, or St. Louis, and of one hundred and twenty- 
nine outbreaks in American cities only two instances were 
reported, namely in Washington, D. C, in which typhoid 
infection was brought in over a railroad. 

Boers, 1 Bruck 2 and Pfuhl 3 have demonstrated the persist- 
ence of typhoid bacilli in butter up to 27 days, but few if 
any outbreaks have been traced to this article of food. 

Mayer 4 states that paratyphoid bacilli will retain their 
vitality in dried human feces for a year and a half. 

No bacteria can grow except in the presence of moisture, 
so an increase of typhoid bacilli on clothing, furniture, wood- 
work, etc., is not to be looked for. The duration of life under 
such conditions is sometimes shorter and sometimes longer 
than it is in the presence of moisture. This will be discussed 
further in another connection. 

It must be confessed that the experimental evidence relat- 
ing to the growth and vitality of typhoid bacilli outside the 
body is by no means conclusive. The evidence seems to be, 
however, that they rarely if ever increase in numbers, and in 
most instances they tend to die off, and that quite rapidly, 
often in a few days, or even hours. 

Epidemiological Evidence. Soil. — There is not much 
epidemiological evidence that typhoid bacilli retain their 
vitality outside of the body for more than a few weeks or 

1 Boers, cited in U. S. Pub. Health and Mar. Hosp. Serv. Hyg. 
Lab. Bull. No. 41, 24. 

2 Bruck, Deutsche med. Wchnschr., 1903, XXIX, 460. 

3 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 
* Mayer, Munch, med. Wchnschr., 1908, LV, 2218. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 13 

perhaps occasionally for a few months, and there seems to 
be no such evidence of their increase, except sometimes in 
milk. Westcott 1 reports an instance where a well continued 
infected for 20 months. It was claimed that the conditions 
were such that continuous infection could not have taken 
place, but this does not appear to have been the fact. 
The numerous instances given in the Report on Typhoid 
Fever in the Spanish War 2 as showing the growth of typhoid 
bacilli in the soil, are by no means conclusive. Infected 
soil was supposed to have caused outbreaks in various 
army corps, but other sources could not be in any case 
excluded, and the chances of other modes of infection in 
an army are very great. The infection was supposed to 
have remained many months, and it is possible that it may 
have in some instances done so. As a matter of fact 90 per 
cent of the volunteer regiments in the Spanish War sooner 
or later became infected whether encamped on a polluted 
site or not. Koch 3 believed from epidemiological as well as 
from bacteriological evidence that it is very rare for an out- 
break to be due to long continued soil pollution, and that the 
possibility of the growth of the bacillus outside the body may 
be neglected. In 1902, Koch undertook the investigation of 
the typhoid fever which had prevailed for some time in sev- 
eral villages in Trier. As a result of his labors, every typhoid 
case and typhoid carrier in four of the villages was isolated, 
and the outbreak ceased, showing that it was due entirely to 
contact infection and not to soil infection. 

Epidemiological Evidence. Water. — Numberless out- 
breaks of typhoid fever have been traced to infected waters. 
In some instances the pollution of rivers is continuous, and 
the cities supplied from them suffer from a uniformly high 

1 Westcott, J. State M. Lond., 1899, VII, 104. 

2 Abstr. of Rep. on the Origin and Spread of Typhoid Fever in 
U. S. Military Camps during the Spanish War of 1898, Wash., 1900, 
206-209. 

• Koch, Die Bekampfung des Typhus, Berl., 1903, 14, 19. 



14 THE SOURCES AND MODES OF INFECTION 

death rate from this disease. In most instances water out- 
breaks are of an explosive character, the onset is sudden and 
they often end suddenly, though sometimes the decline is 
gradual owing to the development of a certain number of 
secondary cases due to contact infection. A few days' or 
sometimes a single day's pollution is sufficient to account 
for the whole outbreak. Three outbreaks of this kind have 
occurred in Providence, and in one instance it was clearly 
traced to the throwing upon the banks of the river of the 
excreta from an infected family. The Providence watershed 
covers about ninety-six square miles, and had upon it in 1900 
a population of some 35,000, a large part in villages along the 
banks, but some scattered in hamlets and farms over the 
whole area. The death rate from typhoid fever in Rhode 
Island is not less than 20 per 100,000 in the country districts, 
which means seven deaths per annum on the watershed. As 
the fatality is not over 10 per cent, there must be seventy 
cases, and if we add the " carriers," the number of persons 
each year distributing typhoid bacilli on the watershed must 
be at least one hundred, and perhaps very much greater. It 
is also certain that disinfection of excreta is practiced to such 
a slight extent as to accomplish very little. The fact that 
for years the city has had no outbreak of disease, and no 
excess due to the water, as is shown by the typhoid death 
rate which for several years has varied from seven to twenty- 
six per one hundred thousand, indicates that the typhoid 
bacilli, which are being continually deposited on the water- 
shed, fail to multiply. Exactly similar conditions prevail on 
the watersheds of Pawtucket, Newport, Woonsocket, Hart- 
ford and New Haven, only to mention those cities in my 
neighborhood with which I am personally familiar. And the 
general testimony of all epidemiologists is that municipal 
water supplies are never continuously infected unless com- 
paratively fresh excreta from typhoid-infected persons pass 
directly and continuously into them. Nevertheless it is cer- 
tain that typhoid bacilli must be continually discharged onto 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 15 

the soil, and we are justified in considering the freedom from 
infection of the surface waters coming from such areas a 
strong evidence that the growth of the typhoid bacillus out- 
side the body does not commonly occur, and is a negligible 
factor in the causation of the disease. 

Cholera. — Early investigators, as Nicati and Rietsch, 
working with sterilized soil and water, found that cholera 
spirilla would live outside the body sometimes as long as 2 
months. But all the more recent workers agree that under 
natural conditions, in unsterilized materials, the life of the 
organism is quite short. Loesner 1 recovered the germs from 
dead bodies, which had been artificially injected, as late as 
the twenty-eighth day. Houston 2 says that they usually die 
off in the surface layers of the soil in 12 days, though they 
may be kept alive longer if the soil is watered with liquid 
manure. Though Heiser 3 states that the spirillum was found 
in the quiet water in the bends of the Passig river, no evi- 
dence was presented to show that it grew there. Gotschlich 4 
states that the spirillum is rarely found in feces for more than 
three days, and quotes Abel and Draer, Claussen and Dun- 
bar, and refers to Koch, as stating that it dies in dirty canal 
water in 24 to 30 hours. In unsterilized milk it may live 
from 1 to 2 days, but dies as soon as the milk becomes sour. 
All these agree that there is not the slightest evidence that 
the cholera spirillum can increase in numbers outside of the 
body. On the other hand, Emmerich and Gemund° claim 
that it does increase in numbers in the soil, and may be found 
for two and one-half months. Paladino-Blandini 6 also states 

1 Loesner, Arb. a. d. k. Gsndhtsamte. Berl., 1896, XII, 448. 

2 Houston, Rep. Med. Off. Local Gov. Bd., Lond., 1898-9, XXVIII, 
413. 

3 Heiser, Philippine J. Sci. (Med.), 1908, III, 92. 

* Kolle u. Wassermann, Handbuch [etc.], Jena, 1904, IV, 108. 

5 Emmerich and Gemund, Miinchen med. Wchnschr., 1904, LI, 1089, 
1157. 

6 Centralbl. f. Bakteriol. [etc.], I, Abt. Ref., Jena, 1905, XXXVI, 53. 



16 THE SOURCES AND MODES OF INFECTION 

that it may grow in polluted soil. Koch 1 says that it grows 
only in the human body. 

Cholera and Soil. — There is certainly a great deal of clin- 
ical evidence that it does not increase in the soil, but on the 
contrary speedily dies out. The epidemic of cholera in 
Europe in 1885 was very widespread in Italy and Spain. 
How extensively it prevailed and what a great number of 
towns and villages were infected are well shown in the excel- 
lent report prepared by Shakespeare. 2 Nevertheless by the 
succeeding year it had entirely disappeared from Spain, and 
largely from Italy. Turkey had a similar experience. 3 We 
know that with the sanitary conditions prevailing in those 
countries at that time the soil must have been infected with 
cholera in countless places. But cholera rarely recurred, and 
when it did, it was in large cities, where, the most probable 
explanation is, it was maintained during the interval by mild 
unrecognized cases or latent infections. The extensive epi- 
demic in the United States in 1873 was not followed by a 
recurrence in the succeeding year. Not only is epidemiologi- 
cal evidence strongly against the saprophytic existence of 
cholera in temperate climates, but it is equally so for tropical 
regions. The great outbreak in the Philippine Islands in 
1902-3 attacked hundreds of villages, and soil infection was 
universal, yet the disease speedily died out all over the islands. 4 
In 1905 there was a similar experience. 

In the Philippine Islands during the latter outbreak 
it was believed that the cooked food offered for sale in the 
streets was a frequent vehicle of cholera germs, and a num- 
ber of samples, particularly of boiled rice, were found to con- 
tain the spirilla. 5 The rice was probably contaminated by the 

1 Koch, Die Bekampfung des Typhus, Berlin, 1903, 14. 

5 Shakespeare, Rep. on Cholera in Europe and India, U. S. Gov. 
Print. Off., Wash., 1890. 

8 Clemow, Tr. Epidemiol. Soc, Lond., 1904, n. s., XXIII, 223. 
4 Woodruff, J. Am. M. Ass., Chicago, 1905, XLV, 1160. 

6 Maus, Med. News, N. Y., 1902, LXXXI, 318. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 17 

hands of sellers or purchasers. Whether the spirilla increased 
in numbers is not known. 

Mediterranean Fever. — Mediterranean or Malta fever 
has long been recognized as endemic at various points on the 
shores of the Mediterranean, particularly on the island of 
Malta. It shows all the characters of " endemic " disease, 
being confined to certain areas and exhibiting little tendency 
to pass to other parts of the world, or to extend by contagion. 
The micrococcus, M. melitensis, which is its cause, was dis- 
covered by Bruce in 1887 and has been very carefully studied 
by an English commission acting under the supervision of 
the Royal Society. This commission, as have independent 
observers, has given much study to the vitality of the spe- 
cific organism of the disease outside of the body. The evi- 
dence seems to be that it tends, like other disease germs, to 
perish when removed from the body and deprived of nourish- 
ment and moisture and exposed to light and heat, but it may 
retain its vitality for weeks and even months under certain 
conditions, behaving in this respect much like the typhoid 
bacillus. 1 No direct experiments seem to have been made to 
determine whether it ever maintains a saprophytic existence 
in the soil, but its habits of life are such that it is a fair in- 
ference that it can rarely do so, and that such saprophytic 
growth, if it ever takes place, is of no greater practical impor- 
tance than is the saprophytic growth of typhoid germs. The 
micrococcus was carefully sought for in water and in dust, 
but was never found. 2 The disease is referred to in this con- 
nection because, on account of its localization and slight 
apparent contagiousness, it was believed by many medical 
men, as well as the laity, to spring from the soil. Yet the 
work of the English investigators has conclusively shown 
that the chief source of the disease is the herds of infected 
goats. It is by the infected milk of these that the disease 
is transmitted to human beings. It is barely possible that 

1 Report of Commission of Royal Society, 1901, Pts. I and II. 
a Bruce, Nature, Lond., 1908, LXXVIII, 40. 



18 THE SOURCES AND MODES OF INFECTION 

the fever may be spread to some extent by contact with 
infected urine either of goats or of men, just as typhoid 
fever frequently extends by contact infection, but the fact 
that thousands of infected men have been invalided home 
to England without any extension of the disease in that 
country would indicate that such occurrence is extremely 
rare. 

Bubonic Plague. — The germ of bubonic plague is not so 
resistant as is that of typhoid fever, nor yet is it of such feeble 
vitality as that of cholera. It is rather susceptible to disin- 
fectants, to high temperature and to drying, but in a moist 
condition, particularly at low or moderate temperatures, may 
remain alive for some months. 1 The endemicity of the dis- 
ease in many localities has led some to assume that it devel- 
ops in the soil, but the most careful students see no necessity 
for assuming soil infection to account for its diffusion, and 
there is ample positive evidence that plague is derived from 
other sources. Yet, in view of the fact that soil infection 
has been so much discussed, it is rather remarkable that so 
few actual experiments have been made to test the theory. 
Perhaps it is because such experiments are difficult and 
those who are most competent to make them have thought 
their time better occupied with work giving better promise 
of positive results. Elliot 2 found that soil naturally infected 
would cause the disease in rats after an interval of a month, 
and Watkins-Pitchford 3 in some careful experiments found 
that inoculated soil retained its virulence for four weeks, but 
not for five weeks. The soil was not sterilized. Gladin 4 
found the bacillus alive in unsterile moist earth after 2 

1 Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. 
Bull. No. 4, 1901. See also Simpson, A Treatise on Plague. 

2 Elliot, Lancet, Lond., 1905, I, 1562. 

3 Watkins-Pitchford, Rep. Gov. Bacteriologist, Pietermaritzburg, 
1903 [Report on Plague, 31]. 

4 Gladin, Centralbl. f. Bakteriol. [etc.], I, Abt. Orig., Jena, 1898, 
XXIV, 588. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 19 

months, and Rosenau l kept it alive a long time in cool moist 
garden earth, and the Indian Plague Commission, 1901, did 
the same in moist sterile cow dung. Other experiments by 
Mackie and Winter in Bombay, cited in the Journal of Hy- 
giene, 2 were with grossly infected cow dung from the floor of a 
native house. No pest bacilli were recovered by culture on 
inoculation after 96 hours. Further careful experiments have 
been made by the Indian Commission of 1905. Their con- 
clusions are as follows: 

"Floors of cow dung grossly contaminated with the bacillus 
of plague remain infective for 48 hours ; floors of a sort of na- 
tive cement for 24 hours, the infectivity being tested in each 
case by inoculation. The floors were infective to animals 
allowed to run on them for only half the above time." 

Thus there appears to be no bacteriological evidence that 
the bacillus of plague grows outside of the bodies of living 
animals, and a great deal of evidence that when separated 
from the body it tends to die off more or less rapidly and fre- 
quently very rapidly. The Indian Plague Commission con- 
siders that reports of soil infections are unworthy of credence 
unless continuous and careful observations on the presence 
of rats and fleas have been made. 

Dysentery Bacillus. — One form of dysentery is caused by 
a bacillus belonging to the colon group, and it has a number 
of sub-varieties. It is not quite so resistant as the typhoid 
bacillus, but it has been known to survive all winter in damp 
earth. 3 It is said that in Japan local outbreaks often persist 
longer than do outbreaks of cholera, perhaps due to the higher 
resistance of the germ. 4 The bacilli appear to be easily de- 

1 Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. 
No. 4, 1901, 9. 

2 J. Hyg., Cambridge, 1906, VI, 511. 

3 Schmidt, Centralbl. f. Bakteriol. [etc.], I, Abt. Orig., Jena, 1902, 
XXXI, 522. 

4 Eldridge, U. S. Pub. Health and Mar. Hosp. Serv. Pub. Health 
Rep., 1901, 1. 



20 THE SOURCES AND MODES OF INFECTION 

stroyed by other bacteria, for they can rarely be found in feces 
after two days. 1 

Dysentery Ameba. — Another form of dysentery occur- 
ring chiefly in the tropics is caused, not by a bacterium, but 
by an ameba, which is one of the lower forms of animal, not 
vegetable life. The researches of Musgrave and Clegg 2 show 
that there are many forms of amebse, probably distinct 
species, and that they grow in the soil and on various kinds 
of vegetables. They can be grown on culture media at room 
temperature and produce the disease in monkeys and men. 
They may become encysted and then are quite resistant 
to drying. The question of the identity of the saprophytic 
and pathogenic amebse, which is maintained by the writers 
just named, is still subjudice. and will be again referred to in 
Chapter II. 

Bacteria of Suppuration. — The formation of pus in wounds, 
abscesses, or elsewhere, is practically always the result of 
infection by bacteria. Very many varieties of bacteria may 
occasionally cause suppuration, but a few species such as 
the Micrococcus aureus, M. albus and M. citreus, and Strep- 
tococcus pyogenes, are by far the most common cause of this 
process. I have never had occasion to pay much attention 
to the habitat of these bacteria, but according to Gotschlich 3 
they are constantly found growing in the skin and on the 
mucous surfaces. References are of course given in his article 
to numerous original investigations, but among more recent 
observations may be mentioned those of Ruediger, 4 Gordon 5 
and Hess. 6 These bacteria are also found in the tonsils and 

1 Kruse, Deutsche med. Wchnschr., 1901, XXVII, 370, 386. 
" Musgrave and Clegg, Bull. No. 18, Bu. Gov. Lab. P. I. 
• Gotschlich, Kolle and Wassermann, Handbuch [etc.], Jena, 
1902, I, 147. 

« Ruediger, J. Am. M. Ass., Chicago, 1906, XLVII, 1172. 

5 Gordon, Rep. Med. Off. Local Gov. Bd., Lond., 1904-5, XXXIV, 
387. 

6 Hess, Centralbl. f. Bakteriol [etc.], I, Abt. Orig., Jena, 1907, 
XLIV, 1. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 21 

lymph glands, apparently remaining latent for long periods 
of time, i.e., not causing suppuration. Bacteria such as the 
above, which are the constant parasites, or perhaps rather 
commensals of man, are naturally to be looked for in the 
vicinity of man and on the surfaces of the body, on clothing, 
utensils, furniture; and the dust and dirt of all places fre- 
quented by human beings are found to contain more or less of 
them. They may also be found in polluted waters. But 
whether under natural conditions they are commonly able 
to maintain a saprophytic existence is another matter. Judg- 
ing from what I have read in the text-books I should suppose 
that the pus organisms are not so limited as to the conditions 
of their growth as are most disease-producing bacteria. They 
are not so dependent on a high and even temperature or on 
the composition of the medium on which they grow. I should 
suppose that they would be more likely to maintain a sap- 
rophytic existence than most other pathogenic organisms, yet 
I do not know that such existence for them has ever been 
demonstrated. In fact Gotschlich 1 says that they are not 
saprophytes. Bacillus pyocyaneus has, however, been found, 
by Gorham, growing in a heap of moist rags at a paper mill. 
Diphtheria. — Diphtheria was not so very long ago believed 
to be a " filth disease," that is, its germs were supposed to 
have a habitat outside of the body in various forms of " dirt." 
This theory was common during my medical-school days, and 
when I began health-department work in 1884, I tried to fit 
the facts as I saw them to this theory. But they did not 
fit, and the impression continued to grow that diphtheria 
was a purely contagious disease. The life habits of the diph- 
theria bacillus indicate that while it is more resistant than 
some other disease-producing organisms next to be men- 
tioned, and somewhat easier to cultivate, it is very unlikely 
that it is able to propagate itself outside of the body, except 
at times in milk. Houston, 2 while he does not consider his 

1 Gotschlich, Kolle and Wassermann, Handbuch [etc.], Jena, IV, 173. 

2 Houston, Loc. Gov. Bd. Rep. of Med. Off., 1898-9, XXVIII, 413. 



22 THE SOURCES AND MODES OF INFECTION 

experiments conclusive, believes that the bacillus of diph- 
theria dies off very quickly in unsterilized soils of various 
kinds. Graham-Smith 1 cites a number of writers concerning 
the vitality of the organism in water and milk. According 
to Seiler and Stoutz, it multiplies in sterilized water for a 
while, but Montefusco and D'Espine and Marignac found 
no evidence of multiplication even in distilled water, and in 
polluted water it dies in 6 days. Schottelius reported, con- 
trary to general experience, that the bacillus multiplies more 
rapidly in raw than in sterile milk, while Montefusco found 
no multiplication in raw milk after 3 days, and Rubinstein 
found that the bacilli died in 24 hours. Eyre showed that 
in milk drawn in as sterile a condition as possible the diph- 
theria like the typhoid bacillus undergoes rapid multiplica- 
tion. Kersten, 2 on the other hand, reports that diphtheria 
bacilli will persist in raw milk for 72 days, and though 
they undergo no increase at first, do so later. Montefusco 
found that they died in fresh bread in 24 hours. Except in 
fairly fresh milk at room temperature, it is unlikely that the 
bacilli of diphtheria multiply outside of the body. 

Other Diseases. — Tuberculosis, pneumonia, influenza, 
cerebro-spinal meningitis, gonorrhea and syphilis are caused 
by organisms which are difficult to cultivate, and I think all 
bacteriologists agree that it is futile to seek for their habitat 
outside of the bodies of men or other animals. As for the 
protozoan diseases, such as malaria and sleeping sickness, 
such a habitat is still more improbable. It is only recently, 
and after laborious experiment, that any of this class of 
organisms have been cultivated in the laboratory. That they 
grow outside of the body under ordinary conditions is in the 
highest degree improbable. There is one protozoan, however, 
the dysentery ameba, which, if recent observations are cor- 
rect, does live outside of the body. But this organism belongs 

1 Nuttall and Graham-Smith, The Bacteriology of Diphtheria, Cam- 
bridge, 1898, 171. 

2 Kersten, Arb. a. d. k. Gsndhtsamte., Berl., 1909, XXX, 341. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 23 

to an entirely different class from the blood parasites, and 
while the facts so far known render it not improbable that 
the ameba does grow outside of the body, the facts in regard 
to blood parasites are against any such hypothesis. 

Summary of Laboratory Evidence. — It appears, then, that 
so far as experimental evidence is concerned there is no war- 
rant for assuming a source for the common infectious diseases 
outside of animal bodies. It is only with extreme difficulty 
that a few of the blood parasites belonging to the protozoa 
can be cultivated, and the cultivation of many bacterial 
forms is strictly limited, so that it is hardly possible to ima- 
gine their maintaining a sapropr^tic existence. It is true 
that the bacteria of typhoid fever and perhaps cholera, dysen- 
tery, and diphtheria may be conceived of as growing outside 
of the body under natural conditions, but such growth, if it 
ever occurs, must be rare. 

Lack of Epidemiological Evidence. — Nevertheless during 
the larger part of the nineteenth century it was common to 
seek such an outside source for most of the infectious diseases. 
The filth theory of disease, the vogue of which was largely 
due to Chadwick, Murchison and Pettenkoffer, assumed that 
the specific poison of many of our common infectious diseases, 
and particularly of typhoid fever and cholera, developed in 
a contaminated soil, or in other forms of filth. There was at 
that time no knowledge of the micro-organisms which cause 
disease, and the theories of the origin of disease, so far as 
they had any basis at all, depended on clinical or epidemio- 
logical evidence. There was, it is true, some epidemiological 
evidence for believing that typhoid fever and cholera could 
develop in filth, for both of these are excrement-borne dis- 
eases, and it was difficult to decide without any knowledge 
of the bacteria which cause them whether they developed 
in filth or were merely transmitted in filth. But as regards 
typhus fever, smallpox, scarlet fever, measles, diphtheria 
and similar diseases, there is really no epidemiological evi- 
dence to suggest that they develop outside of the body. If 



24 THE SOURCES AND MODES OF INFECTION 

a disease does have its source in the outer world, we should 
expect to find it localized, attached to a definite locality, 
endemic, as it was formerly called. The somewhat well-de- 
fined infected area we should expect to maintain its infection 
for some time, and we should expect persons coming into the 
area to become infected. But if we watch the outbreaks, 
especially the smaller outbreaks, of such diseases as measles, 
smallpox, scarlet fever, diphtheria, etc., which occur in dif- 
ferent sections of cities, or in villages, we find nothing to 
indicate place infection. A " pin map " of these diseases in 
a city shows first one or two pins, indicating infected houses, 
then more appearing day by day in the surrounding section, 
until there are ten or twenty or a hundred cases within 
the radius of a block or a few blocks or half a mile. The 
scattered groups of houses are of a somewhat circular form, 
a little denser nearer the center. The outbreak lasts a few 
weeks, or two or three months, and then disappears, only to 
reappear in another part of the city. In village outbreaks 
contagion is usually more clearly traced. The importation 
of the disease and the sequence of the earlier cases are often 
made out. The outbreak lasts only for a moderate time, and 
then the disease disappears, usually not to return for a con- 
siderable time, often for years. There is nothing to indicate 
soil infection. If these diseases really come from privy 
vaults, sink drains and garbage heaps, we should expect a 
very different distribution in the house from what is actually 
found. The ground floor is not oftener infected than the 
upper floor, nor (for some might say that rising currents carry 
disease germs to the top of the house) the upper than the 
lower. But what is most important, when one family in a 
house is attacked with such a disease as diphtheria, we should 
expect the other families to be usually attacked also, if the 
disease is a disease of locality. But in Providence statis- 
tics for the last twenty years show that in scarlet fever and 
diphtheria in only about seven per cent of the houses does 
the disease extend from one family to another. In most of 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 25 

these cases of extension, direct contact between members of 
the families is shown to have taken place. 

In such important diseases as smallpox, measles and scarlet 
fever, the germs of which have not been isolated, as well as 
in typhus fever, diphtheria and whooping cough, epidemio- 
logical evidence of an extra-corporal origin is entirely lack- 
ing. Epidemiological and laboratory evidence are against 
the growth of disease germs outside of the body under 
ordinary circumstances. The notion still common, even 
among physicians and health officers, that these infectious 
diseases are filth diseases, as that term is ordinarily under- 
stood, is absolutely without foundation. 

Typhoid Fever and Cholera. — Typhoid fever and cholera 
not infrequently appear in small contact outbreaks very 
similar to those of scarlet fever and diphtheria, but being 
excrement-borne, contact infection is not so common as in 
the latter, while infection by water and food is more common. 
Some outbreaks of typhoid fever may undoubtedly be inter- 
preted as due to soil infection, but they can also be explained 
otherwise, and the bacteriological evidence is so strongly 
against the soil hypothesis that we are not justified at 
present in assuming it. There is no evidence that cholera 
finds a habitat in the soil of temperate climates, and the 
most careful observers in the tropics are, I think, agreed 
that it is not different there. The same is true of bubonic 
plague. 

Yellow Fever and Malaria. — There is a class of diseases 
for which there seemed, at one time, to be very strong evi- 
dence that the cause which produced them had its origin out- 
side of the body. I refer to yellow fever, malaria, sleeping 
sickness and the blood-parasite diseases of cattle. Malaria 
is one of the best defined, oldest, and best understood of 
diseases. I suspect that for twenty-five hundred years what 
has been known of malaria has decidedly colored prevailing 
views as to the nature and source of many other infectious 
diseases. Malaria is a typical endemic disease. Its localiza- 



26 THE SOURCES AND MODES OF INFECTION 

tion can scarcely be better illustrated than in my own neigh- 
borhood. During the latter half of the nineteenth century 
the southern part of New England suffered from extensive 
outbreaks of malarial disease. The whole country was by no 
means affected, but well-defined limited areas of infection were 
to be noted all over the region, and in different portions of 
some of the cities. Infection in many of these persisted from 
year to year. People moving into them became sick, and 
malaria was escaped by moving away. Most of these areas 
were in close proximity to swampy land and marshes, others 
were some little distance removed, but usually in the direc- 
tion of the prevailing winds. Thus there was presented a 
perfect picture of place infection. We were justified, in the 
then existing state of knowledge, in assuming that the mala- 
rial poison developed in the wet and marshy places which 
were closely connected with these infected spots. We now 
know that this assumption was incorrect, though it was very 
near the truth, and that the germs of malaria do not 
develop in the marshes, but that the mosquitoes which 
carry the germs from one person to another do breed 
there. As far as sanitation was concerned the error was 
not serious. The new facts have simply enabled us to 
work more economically, by determining accurately just 
what wet places are dangerous. But the apparent certainty 
that the malarial virus developed outside of the body had 
enormous influence in encouraging the belief that other 
disease poisons also had an extraneous origin. The history 
of yellow fever is somewhat similar to that of malaria. It is 
eminently a place disease. So are sleeping sickness and Texas 
cattle fever and a number of other diseases. All of this group 
we now know are transmitted by insects, and it is the insects 
which have an extraneous existence and not the parasite of 
the disease. The mico-organisms which cause these diseases 
do not grow outside of the bodies of human beings or other 
animals which serve as hosts, or of the insects which serve as 
carriers. 



LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 27 

Review of Evidence. — In reviewing this subject we are 
forced to the conclusion that while it is possible that the 
anthrax and tetanus bacilli and the pus-forming bacteria 
may develop in the soil, there is no evidence that they com- 
monly do so. It is also possible that the typhoid bacilli, and 
to a still less extent the bacteria of cholera, dysentery and 
plague, maintain a limited saprophytic existence, but this is 
probably very unusual. There is ample epidemiological evi- 
dence that in temperate climates such a source for these 
diseases must be an almost infinitesimal factor in their 
development. Probably the diphtheria bacillus never has a 
saprophytic growth of any significance, unless possibly very 
rarely in milk. As for tuberculosis, pneumonia, influenza, 
cerebro-spinal meningitis, scarlet fever, typhus fever, small- 
pox, whooping cough, gonorrhea and syphilis, malaria, yellow 
fever and sleeping sickness, there is not the slightest reason 
for supposing that they ever develop outside of the bodies of 
animals. 

Changes in Present Theories and Practice. — If these facts 
are correct — and I can scarcely believe that any will seriously 
contend that we have any evidence that an appreciable 
amount of our common infectious diseases arises in the exter- 
nal world — prevailing notions as to the sanitary functions of 
the state should be decidedly modified. The laity and the lay 
press still believe that most of the infectious diseases have 
their origin outside of the body, in filth, or if admitting con- 
tagion, attach equal importance to external sources of infec- 
tion. And even very many health officials and some teachers 
and writers on sanitation hold the same view. Municipal 
sanitation and municipal cleansing are still synonymous 
terms to many health officers. It is true enough that two or 
three diseases, as typhoid fever and cholera, the germs of 
which are found in human excrement, have markedly dimin- 
ished as a result of improved methods of excrement disposal, 
or because of the introduction of water supplies uncontami- 
nated with human excrement. It is also doubtless true that 



28 THE SOURCES AND MODES OF INFECTION 

whatever promotes municipal cleanliness tends to promote 
personal cleanliness, and real personal cleanliness, as we 
shall see, is doubtless an important factor in the preven- 
tion of contagion. But except for one or two diseases, 
and except for very indirect effects, the cleansing of streets, 
alleys, and back yards, of dwellings and stables, the regula- 
tion of offensive trades, and the prevention of nuisances 
generally, have, so far as we can see, no relation to the general 
health, nor any value in the prevention of specific diseases. 
While municipal improvements such as the above are desir- 
able, there is little more real reason why health officials 
should work for them, than there is that they should work 
for free transfers, cheaper commutation tickets, lower prices 
for coal, less shoddy in clothing or more rubber in rubbers, — 
all good things in their way and tending towards comfort and 
health. 



CHAPTER II. 

CARRIERS AND MISSED CASES. 

A Recent Discovery. — That there are occasionally seen 
mild cases of the infectious diseases difficult or impossible to 
recognize, has long been known. That such cases are rare 
has always been generally believed. That the germs of dis- 
ease can maintain themselves and increase in number in a 
person without causing any symptoms at all, was until 
recently scarcely thought possible, and the idea that such 
latent infections are extremely common would have been 
scouted as preposterous. Even to-day the facts are denied 
by many sanitary officials, and there are comparatively few 
who recognize the frequency with which mild atypical forms 
of disease and healthy " carriers " of germs are found, or 
realize the tremendous importance which such cases have in 
the spread of the contagious diseases. Undoubtedly the most 
fruitful medical discovery of the last century, and perhaps of 
all time, was the discovery of the parasitic nature of the 
infectious diseases. Probably the most important discovery 
bearing on preventive medicine since the demonstration of the 
bacterial origin of disease, is that disease germs frequently 
invade the body without causing disease. The succeeding 
pages will be devoted to a consideration of some of the data 
available concerning the existence of mild cases and carriers. 
The term " carrier" is applied to those persons in whom patho- 
genic micro-organisms exist, but who, nevertheless, show no 
symptoms. Such carriers are rarely found by the health offi- 
cer, and the very mild cases also naturally escape notice and 
are hence called by the English " missed cases," i.e., cases 
which fail of recognition. 

29 



30 THE SOURCES AND MODES OF INFECTION 

Typhoid Fever not an Intestinal Disease. — Bacteriolo- 
gists are coming to look upon typhoid fever as essentially an 
infection of the blood rather than a disease of the intestines. 
Frequently the intestinal lesions are slight, and often the 
bacilli are few in number in the feces, and sometimes they 
cannot be found at all. Semple and Greig l report a case of 
typhoid fever in which the bacilli were found in the blood 
from July 20th to September 20th, but were never once found 
in the feces or urine. 2 So far as we know, the typhoid bacil- 
lus may enter the lymph and blood from any portion of the 
alimentary canal, and Semple and Greig, Forster, Kayser and 
others believe that it frequently enters through the tonsils, and 
Pratt, Peabody and Long 3 say that there is no more evidence 
of entrance through the intestines than through the tonsils. 
In any event the bacillus is soon found in the blood, and con- 
tinues in this fluid through the acute stages of the disease. 
Typhoid fever is, then, as was first pointed out by Schott- 
miiller in 1902, essentially a bacteremia. The bacillus may 
migrate from the blood to any organ. As has been shown by 
Pratt, Peabody and Long, a favorite habitat is the gall blad- 
der. Pratt found it in the gall bladder in twenty-one out of 
thirty cases. It may also infect the bones, 4 kidneys, 5 ovaries, 5 
urinary bladder, cerebro-spinal fluid, 6 and maybe found in the 
bronchial secretions (Pratt, Peabody and Long cite several 
authors as to the finding of the bacillus in bronchial mucus, 
and state that Dieudonne found it for seven weeks after 
recovery). Some of these cases give no evidence of intestinal 

1 Semple and Greig, Scient. Mem., Med. and Surg. Dept., Gov. of 
India, 1908, XXXII, 9. 

2 See also Opie and Bassett, cited by Pratt, Peabody and Long. 

3 Pratt, Peabody and Long, J. Am. M. Ass., Chicago, 1907, XLIX, 
846. 

4 Sultan, Deutsche med. Wchnschr., 1894, XX, 675. 
6 Greaves, Brit. M. J., Lond., 1907, II, 75. 

6 Lavenson, Univ. Penn. Med. Bull., 1908-9, XXI, 55; Silber- 
berg, Berl. klin. Wchnschr., 1908, XLV, 1354. 



CARRIERS AND MISSED CASES 31 

infection. Ludke 1 experimenting with guinea pigs showed 
that typhoid bacilli may remain latent in the spleen and bone 
marrow for some time. Kelly 2 says that typhoid bacilli 
were found in 7 of 77 gall-bladder operations, and he states 
that in many cases there is no evidence of intestinal 
infection. Primary cholecystitis has also been reported 
by others. 

Typhoid Bacilli in Urine. — That typhoid bacilli may per- 
sist in the body without causing symptoms has been known 
for some time, but the importance of this fact has been recog- 
nized only during the last few years. When the gall bladder 
or the urinary tract is the seat of the persistent infection, 
the bacilli may be discharged in the feces or urine. Richard- 
son 3 has shown that twenty-three per cent of all typhoid fever 
patients after recovery have typhoid bacilli in their urine, 
often in pure culture and usually in large numbers, but they 
generally disappear within three months. Long-continued 
urinary infection, however, does sometimes occur. Thus 
Houston 4 and Cochrane 5 found the urine infectious for three 
years. 

Typhoid Bacilli in Feces. — Typhoid bacilli can often be 
recovered from the feces after recovery, as well as from the 
urine. Graham, Overlander and Dailey 6 found the bacilli in 
the feces of 11, or 16.9 per cent, of 65 patients 10 days pre- 
vious to their discharge from the hospital. Semple and Greig 
found that 11.6 per cent of 86 typhoid convalescents dis- 
charged bacilli in their feces for over 6 weeks. It is probable 
that the infection generally disappears from the majority of 
cases, but some become " chronic carriers/' and the bacilli 
may often be found in enormous numbers in the feces for 

1 Ludke, Miinchen med. Wchnschr., 1908, LV, 1369. 

2 Kelly, Am. J. M. Sc. Phila., 1906, n. s., CXXXII, 447, 744. 

3 Richardson, J. Exper. M., N. Y., 1898, III, 349; 1899, IV, 19. 

4 Houston, Brit. M. J., Lond., 1899, I, 78. 

5 Cochrane, J. Roy. Army Med. Corps, Lond., 1909, XII, 155. 

8 Graham, Overlander and Dailey, Bost. M. & S. J., 1909, CLX, 38. 



32 THE SOURCES AND MODES OF INFECTION 

years. Four and one-half years is the longest time that 
typhoid bacilli have been shown on bacteriological evidence 
to have persisted in the feces. There is, however, epidemio- 
logical evidence for assuming a much longer continuance of 
the infection. Dean l reports the case of a medical man who 
had had typhoid fever twenty-nine years before, and had 
since then frequent attacks of biliary colic. Typhoid bacilli 
were recovered from his feces. It was believed that no one 
had contracted the disease from him, but he had always 
been very careful in his personal habits. Huggenberg 2 
noted thirteen cases in a household extending over a 
period of thirty-two years. One woman who had the disease 
in 1877 was shown to be a*] carrier in 1908. Scheller 3 re- 
ported thirty-two cases extending over a period of fourteen 
years, all probably due to a carrier who had been sick seven- 
teen years before. Gregg 4 found a woman whose blood gave 
a positive Widal reaction, and in whose feces bacilli were 
found, and who had had typhoid fever fifty-two years before. 
She had presumably infected seven persons. Jundell's case 
reported below was infectious perhaps for fifty-four years. 
Chalmers's case ° had had the disease sixteen years before. 
Frosch 6 reports that evidence was presented to the commis- 
sion appointed by the Prussian Government to study this 
subject as follows: That fourteen carriers had been infective 
four tb nine years, six for ten to twenty years, and five for 
from twenty-one to thirty years. Soper's case has now been 
infectious for eight years, and a number of other writers report 
instances of carriers who were presumably excreting bacilli 
more or less constantly for periods of from four to eight years. 

1 Dean, Brit. M. J., Lond., 1908, I, 562. 

2 Huggenberg, Cor.-Bl. f. Schweiz. Aerzte, 1908, XXXVIII, 622. 

3 Scheller, Centralbl. f. Bakteriol. [etc.], I, Abt. Orig., Jena, 1908, 
LXVI, 385. 

^ Gregg, Boston M. & S. J., 1908, CLIX, 80. 

6 Chalmers, Rep. of Med. Off. Health, Glasgow, 1907, 61. 

« Frosch, Klin. Jahrb., Jena, 1908, XIX, 537. 



CARRIERS AND MISSED CASES 33 

Typhoid Bacilli in Persons Never Sick. — Not only are per- 
sons who have had typhoid fever often found to be " carriers " 
of the germs, but persons who have never had the disease 
may be infected. Allowance must, however, be made for 
failure to recognize and remember mild atypical attacks, and 
some of the chronic carriers who are said never to have been 
sick may have forgotten an attack of "grip" or "malaria" 
years before. Soper's case so far as known had never had the 
disease. Houston's case, which had the bacilli in the urine 
for three years, had not been sick. One of the carriers, the 
source of several cases discovered by Semple and Greig, had 
never had typhoid fever so far as known. Roscoe 1 reports 
an outbreak of twelve cases in an insane asylum due to con- 
tact with a carrier who had never had the disease. Jundell 2 
notes a series of twenty-two cases on an estate in Sweden 
occurring at intervals since 1854. The grandmother of the 
family, who had never had typhoid fever, was shown to be 
excreting the bacilli from 1904 until tlie time of the report, 
1908. 

Carriers among Contacts. — Persons brought into intimate 
relation with the sick may become infected without exhibit- 
ing any symptoms whatever. Drigalski and Conradi 3 found 
the infection in 4 healthy persons in contact with typhoid 
cases. Liefmann and Nieter 4 found 7 carriers out of 252 
persons examined in an insane asylum, some of whom it was 
believed were carriers and the causes of the outbreak in the 
institution, but some of them, however, were true contacts. 
Scheller 5 examined 40 persons who drank the milk handled 
by the carrier already referred to. Of these 5 were sick, and 
13 others, who had no symptoms whatever, were yet found 

1 Roscoe, Lancet, Lond., 1909, II, 1137. 

2 Jundell, Abst. J. Am. M. Ass., Chicago, 1909, LII, 388. 

3 Drigalski and Conradi, Ztschr. f. Hyg. it. Infectionskrankh., 
Leipz., 1902, XXXIX, 283. 

4 Liefmann and Nieter, Miinchen med. Wchnschr., 1906, LIII, 2097. 
6 Griffith, Med. Press & Circ, 1905, LXXIX, 208. 



34 THE SOURCES AND MODES OF INFECTION 

to be excreting typhoid bacilli in either feces or urine or 
both. All of them became free from germs within a few 
weeks. 

Carriers during Incubation. — Cler and Ferazzi 1 during a 
food outbreak of typhoid fever found that 6 of 39 persons who 
had eaten the food, though exhibiting no symptoms, were 
carrying the bacilli in their intestines. These " temporary 
carriers " may become sick later, and sometimes the period 
of incubation, so called, may be three or four weeks or even 
longer. 2 Indeed it is not rare to find typhoid bacilli in the 
feces during the period of incubation. During the Spanish 
War typhoid germs were found in the feces during the incu- 
bation period. 3 Conradi also noticed the same thing, and 
considers it an important factor in the spread of the disease. 4 
Ravenel and Smith 5 have reported an outbreak of forty cases 
due to contact with a case before the symptoms had devel- 
oped. There can be no doubt that many persons are 
excreting typhoid bacilli for a variable time while they are 
coming down with the disease, that from fifteen to twenty- 
five per cent continue to excrete them for a number of 
weeks after recovery, and that a small number continue 
to excrete them indefinitely in the feces, or more rarely 
in the urine. These chronic cases are of the greatest 
importance from a public health standpoint, as they are the 
least likely to be discovered and are the most difficult to 
control. It is very desirable to form some estimate of how 
numerous they are. 

Percentage of Carriers. — The earliest investigation of this 
subject was by the Germans. Carriers are defined by Kut- 
scher as persons in whom bacilli persist for more than ten 

1 Cler and Ferazzi, Centralbl. f. Bakteriol [etc.], Jena, I Abt., Ref. 
1905, XXXVI, 479. 

J Griffith, Med. Press & Circ., 1905, LXXIX, 208. 

3 Abst. of Rep. on Origin and Spread of Typhoid Fever in U S. 
Military Camps during Spanish War of 1898, Wash., 1900, 184. 

4 Conradi, Deutsche med. Wchnschr., 1907, XXXIII, 1684. 

5 Ravenel and Smith, J. Am. M. Ass., Chicago, 1909, LII, 1635. 



CARRIERS AND MISSED CASES 35 

weeks after convalescence. By averaging the results obtained 
by Lentz, Klinger and Drigalski, it appears that of 1982 cases 
of typhoid fever 53, or 3 per cent, became chronic carriers. 1 
Park 2 examined the feces of 52 cases, eight months after re- 
covery and found bacilli present in 2; in one of them, however, 
it was present in only one of three tests. Of 16 other persons 
who had the disease six months previously 2 were carriers. 
He thinks that two per cent of all typhoid fever cases become 
permanent carriers, and these may be found in the popula- 
tion at the rate of about one to five hundred. Frosch 3 gives 
a tabulation of 6708 cases of typhoid fever, of which 310, or 
4.62 per cent, continued to excrete bacilli for over ten weeks, 
64 continued carriers for from three months to one year, 87 
for one to three years and 15 for three and one-half years. 
Bruckner 4 states that of 316 persons who had the disease, 12, 
or 3.8 per cent, became carriers, or, omitting the 104 children, 
only 1 of whom was a carrier, and who rarely become such, 
5 . 2 per cent continued to excrete bacilli . Recently Hamilton, 5 
following the suggestion of Gaehtens, tested the opsonic index 
of 25 persons who had gall-bladder trouble and found 7 with 
an abnormally high index. All 7 proved to be carriers. She 
hopes that this will prove a simple means of discovering 
carriers. 

Carriers among the Public. — There have been a few 
studies to determine the number of carriers in the general 
population. Minelli 6 found 1 carrier in 250 prisoners in 
Strasburg. The most extensive investigation has recently 
been carried on in Washington, 7 where the feces from 986 

1 U.S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 35, 169. 

2 Park, J. Am. M. Ass., Chicago, 1908, LI, 981. 

3 Frosch, Klin. Jahrb., Jena, 1908, XIX, 537. 

4 Bruckner, Arb. a. d. k. Gesundhtsamte., Berl., 1910, XXXIII, 435. 
6 Hamilton, J. Am. M. Ass., 1910, LIV, 704. 

6 Minelli, Centralbl. f. Bakteriol. [etc.], Jena, I Abt. Orig., 1906, 
XLI, 406. 

7 U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 52, 
13, 145. 



36 THE SOURCES AND MODES OF INFECTION 

well persons were examined bacteriologically. Only one 
test was made for each person, and 3 carriers were found. 
These were subsequently re-examined and 2 proved to be 
negative. 

Intermittent Excretion. — It seems probable that the num- 
ber of carriers is really larger than the above figures indicate. 
There is no doubt that many carriers do not excrete bacilli 
continuously. Davies and Hall * called attention to the 
marked intermittency of bacillus excretion in their case, re- 
ported previously by Davies, and which will be again referred 
to. This patient had been infectious at times for four years, 
particularly in the spring, and on one occasion she was her- 
self sick. Semple and Greig report several instructive cases. 
One of their cases gave only negative tests for thirty-one days, 
followed by a positive; another carrier remained free from 
bacilli, as shown by daily examination, for a period of seventy- 
five days, and other cases for lesser periods. Scheller noted 
considerable intermittency in the excretion of bacilli. Of 108 
examinations of urine and feces from 18 carriers, only 48 
were positive. This intermittency, coupled with the difficulty 
of finding the bacillus when it is certainly present, renders it 
probable that carriers are frequently overlooked, and makes 
it extremely difficult to apply bacteriological examinations in 
public health work. 

Carriers Cause Disease. — That these carriers can be the 
source of disease in others has been amply demonstrated. 
When I began to write this chapter nearly three years ago, I 
was intending to include references to all outbreaks reported 
as due to carriers, but such reports are now so frequent that 
this is scarcely possible. A good resume of previous literature 
may be found in the United States Public Health and Marine 
Hospital Service Bulletin 35. A number of additional in- 
stances of infection by carriers have already been noted. 
Among the most interesting and well known of these is that 

1 Davies and Hall, Lancet, Lond., 1908, II, 1585. 



CARRIERS AND MISSED CASES 37 

reported by Soper l of a cook who infected twenty-six persons, 
living in six families residing in five localities, in three states. 
The infections took place between 1901 and 1906. The cook 
gave no history of having had typhoid fever, but her feces 
were swarming with bacilli. She was then placed in isolation 
in a contagious hospital. In 1908 an attempt was made in 
the courts to secure the release of " Typhoid Mary " as she 
is called, but it was unsuccessful. What result is secured by 
keeping her in confinement, other than the placing of dis- 
credit on public health work, it is difficult to see. 

Milk and Contact. — The handling of milk by carriers is 
especially dangerous to the public. Kayser, Cameron, 2 Schel- 
ler, Chalmers, Davies, Lumsden and Woodward, 3 Albert 4 
and others have reported outbreaks due to milk infected in 
this way. In the case reported by Albert the bacilli were in 
the urine of a milker who had been sick a year before. In- 
stances of contact infection in insane asylums have been 
reported by Nieter and Liefmann, Levy and Kayser, Friedel, 
Dehler, C. Neisser 5 and Ledingham. 6 Dehler 7 removed the 
gall bladder from two carriers who were found to be the 
cause of the outbreak, and their feces were afterwards free 
from bacilli. Loele, 8 however, opened the gall bladder in a 
convalescent typhoid case which was excreting bacilli, but no 
trace of them could be found in the gall bladder. 

Carrier at Bristol. — A very interesting case is reported by 
Davies, 9 of Bristol, England. A woman had typhoid fever 
in 1901. In 1904 she became the cause of a severe outbreak 
in a girls' school, and in 1907 of another outbreak in another 

1 Soper, J. Am. M. Ass., Chicago, 1907, XLVIII, 2019. 

2 Cameron, Pub. Health, Lond., 1909, XXII, 243. 

3 Lumsden and Woodward, J. Am. M. Ass., Chicago, 1909, LII, 749. 
* Albert, Am. J. Pub. Hyg., 1909, XIX, 260. 

6 C. Neisser, Psychiat.-neurol. Wchnschr., Halle, 1908-9, X, 37. 

6 Ledingham, Brit. M. J., Lond., 1908, I, 15. 

7 Dehler, Munch, med. Wchnschr., 1907, LIV, 779, 2134. 

8 Loele, Deutsche med. Wchnschr., 1909, XXXV, 1429. 

8 Davies, Proc. Roy. Soc. Med., 1908, I, Epidemiol. Sec, 224. 



38 THE SOURCES AND MODES OF INFECTION 

institution where she handled the milk which was proved to 
be the vehicle of infection. It is noteworthy that of seven 
examinations of the feces of this carrier, in five no bacilli 
were found ; and of these, four were successive, from January 
20 to March 14. This indicates that negative results from 
such examinations are of little value. 

The Spanish War investigation showed that most of the 
volunteer regiments were infected when they came to camp, 
that is, they must have contained carriers or mild cases, and 
it was by extension from these that most of the true typhoid 
fever later developed. 1 The distinction between a case of 
true typhoid fever of mild type and a carrier often cannot in 
practice be made. There is no sharp line of demarcation, 
but infection by typhoid bacilli may result in a series of cases 
presenting gradation from the most severe symptoms to none 
at all. It is most unwarranted to assume, as some appear to 
do, that a mild unrecognized walking typhoid case may start 
up an outbreak, but that a true carrier cannot do so. 

Atypical Typhoid Fever. — There can be no question that 
mild unrecognized cases of typhoid fever are extremely com- 
mon. Greater care in diagnosis has made an apparent increase 
in the number of reported cases of this disease, and a decrease 
in the fatality. Thus in my own city the reported fatality from 
typhoid fever has during the last twenty years been reduced 
from 50 to 12 per cent; and it is probably really considerably 
less than that. I have noticed that in milk and water out- 
breaks, when public attention is directed strongly towards 
the disease, the case fatality is often very low, which merely 
means that most of the cases have been recognized. In the 
Spanish War the committee of investigation believed that the 
number of cases actually existing amounted to 20,738, while 
the number reported by the army surgeons was only 10,428. 

Recently Bates 2 has reported a series of mild atypical 

1 Abstr. of Rep. on the Origin and Spread of Typhoid Fever during 
the Spanish War of 1898, Wash., 1900, 168-175. 

2 Bates, J. Am. M. Ass., Chicago, 1908, L, 585. 



CARRIERS AND MISSED CASES 39 

typhoid fever cases in Panama Canal Zone, and states that 
such cases are quite common there, and are the chief factor 
in the extension of the disease. At the time Koch made his 
investigation of the four Trier villages there were 8 recognized 
cases, but a thorough bacteriological investigation of sus- 
pects discovered 64 more. Of these 49 were children. 1 These 
mild unsuspected walking typhoid cases not rarely result in 
death. Velich 2 notes 36 such cases, and a number of others 
are reported by Curschmann, and they also have been seen 
by the writer. I have recently investigated two milk out- 
breaks, in one of which the cause was apparently a mild un- 
recognized case, and in the other either a convalescent or a 
carrier associated with him. Neufeld 3 devotes considerable 
space to this class of cases. 

Paratyphoid. — Rimpeau 4 found paratyphoid bacilli in 3 
of 50 healthy school children, and in 1 of 50 orphans. Only 
one examination of the feces was made. Savage, 5 who has 
devoted much attention to the distribution of this bacillus, 
did not find it in 12 healthy persons. He believes that the 
disease does not spread among human beings like typhoid 
fever, but is usually derived from the lower animals by the 
ingestion of infected food. 

Cholera Spirilla in Convalescents. — According to Kolle, 6 
cholera spirilla are sometimes found in the intestines of con- 
valescents as long as 48 days. Rommelaere 7 reported a case 
retaining the infection 47 days. Forrest 8 found the germs 
remaining 6 weeks. Kirchner 9 says that the spirilla are some- 
times carried for weeks or months. Most observers, however, 

1 Koch, Die Bekampfung des Typhus, Berl., 1893, 14-15. 

2 Velich, Arch. f. Hyg., Miinchen u. Leipz., 1904, XLIX, 113. 

1 Kolle u. Wassermann, Handbuch [etc.], Jena, 1903, II, 271. 

* Rimpeau, Deutsche med. Wchnschr., 1908, XXIV, 1045. 

6 Rep. Med. Off. Local. Gov. Bd., Lond., 1908-09, XXXVIII, 316. 

6 Kolle, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1895, XVIII. 

7 Rommelaere, J. de med., Brux., 1892, XCIV, 837. 

8 Forrest, J. Trop. M. [etc.], Lond., 1908, XI, 321. 
8 Kirchner, Klin. Jahrb., Jena, 1908, XIX, 473. 



40 THE SOURCES AND MODES OF INFECTION 

find that they disappear in a few days. Pfeiffer 1 reviews the 
literature, and cites Simond's observation that the average 
duration of infection is only about 6 days, and that the 
longest seen by him was 18 days. Of 117 cases reported 
to Rumpel not one carried the germs over 24 days. Abel and 
Claussen found the average of 17 cases to be 5 or 6 days, and 
Pfeiffer the average of 39 cases 10 days, though in 2 the infec- 
tion persisted 23 days. Other writers have made similar 
observations. 

Spirilla in Healthy Persons. — Dunbar 2 was the first to 
note the occurrence of cholera spirilla in the feces of healthy 
persons. He discovered 28 healthy carriers in Hamburg 
in 1892-93. Rommelaere noted such a carrier in 1892, and 
carriers are by Koch considered an important factor in 
the spread of the disease. In 1905 cholera seemed to have 
been brought down the rivers from Russia into Germany 
by raftsmen, and Kirchner says that of 27 persons on one 
raft 2 were carriers. Pfeiffer states that in this outbreak 
there were 174 cases of the disease, and that 38 other carriers 
were discovered. He cites Frosch as discovering 16 carriers, 
of whom 12 were children, and Friedheim as finding 51. In 
one family observed by Pfeiffer 4 died, 1 was very sick, 1 
was mildly sick, and 2 were carriers. He says that there are 
very many mild cases of the disease which can only be recog- 
nized bacteriologically. McLaughlin 3 found 17, or 6.44 per 
cent of 264 prisoners in Manila, to be carriers, and in the city 
27, or 7.18 per cent of 376 persons examined. Gotschlich 4 
examined pilgrims returning from Mecca, and though cholera 
had not so far as known prevailed among them, he found 
several Russian and Turkish pilgrims who proved to be car- 
riers of the spirilla. According to Pfeiffer these spirilla of 

1 Pfeiffer, Klin. Jahrb., Jena, 1908, XIX, 483. 

2 Dunbar, Mod. Med., Osier, Phila. & N. Y., 1907, II, 720. 

3 McLaughlin, J. Am. M. Ass., Chicago, 1909, LII, 1155. 

* Gotschlich, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1906, 
LIII, 281. 






CARRIERS AND MISSED CASES 41 

Gotschlich have been carefully studied by a number of ob- 
servers and show slight variations from the type, and have 
probably lost their virulence. Yakovlew, Zabolotny, Zlato- 
goreff and Koulecha l state that in St. Petersburg the feces 
from 2440 apparently well persons were examined, all of 
whom had been more or less in contact with cholera cases. 
Of these 125 contained the cholera spirillum, of which 40 
were from what proved to be mild unrecognized cases, 25 
from persons who were incubating the disease, and 60 were 
from true carriers. Pfeiffer reports several instances in which 
the disease was spread by carriers. 

Chronic Plague in Rats. — Bubonic plague is a disease 
which attacks not man alone but many other species of ani- 
mals, particularly the rat. In fact it may be considered 
primarily a rat disease, and without doubt the rat is the most 
important agent in its diffusion. That mild cases and chronic 
cases exist among rats which superficially appear not to be 
sick, seems to be proved. Simpson 2 says chronic plague was 
observed in some of the animals experimented on in Hong 
Kong, and by Albrecht and Ghon in experimental guinea 
pigs, and in rats for months by Kolle and Martini. The 
Indian Plague Commission (1905) 3 found eleven of the rats 
which they had fed with plague bacilli to be infected, although 
they appeared to be perfectly well. While chronic plague has 
been seen in laboratory animals, several observers in Bom- 
bay and Sydney have failed to find it under natural condi- 
tions, as also did Blue in San Francisco. 4 But Hunter found 
rats with chronic plague in Hong Kong, and the Indian 
Plague Commission (1905) found a number of rats infected 
with plague at a time when no rats with acute plague could 
be discovered, and when there was no outbreak among human 

1 Yakovlew, Zabolotny, Zlatogoreff and Koulecha, Bull. Soc. path, 
exot., Par., 1909, II, 276. 

2 Simpson, A Treatise on Plague, Cambridge, 1905, 129. 

3 J. Hyg., Cambridge, 1907, VII, 379. 

* Blue, J. Hyg., Cambridge, 1909, IX, 1. 



42 THE SOURCES AND MODES OF INFECTION 

beings. The infected rats showed no sign of sickness. 1 Wat- 
kins-Pitchford 2 found the bacillus in convalescent rats and 
guinea pigs. It is evident that such chronic " carriers" may 
be an important factor in the maintenance and extension of 
the disease. 

Atypical Human Plague. — Among human beings mild 
cases of the glandular type are by no means uncommon. 
But fortunately these are rarely dangerous, for without 
suppuration there is no escape of bacilli. But in certain in- 
stances, later suppuration may take place, or lung symp- 
toms develop, so that the individual may become a focus of 
infection. 3 Rat "carriers," on the other hand, are always 
dangerous, for they may at any time suffer accidental death, 
and their carcasses may then readily infect other animals 
and even man. 

Plague Bacilli in Convalescents. — In the pneumonic type 
in human beings the bacilli are thrown off in large numbers 
from the lungs. Martin, 4 Gotschlich 5 and others have found 
them in the sputum up to 76 days after the attack, or 42 
days after recovery. Gaffky 6 cites Vagedes as reporting 
pulmonary infection lasting 2 months in a case in Oporto, and 
bacilli in an abscess persisting more than 2 months, and Vages 
one lasting 4 weeks in Paraguay. The latter also isolated the 
bacilli from a man who later became sick with the disease. 
Shottelius found the germs in the bronchial secretion of mild 
ambulant cases. It is thus very probable that mild cases 
and true carriers among both rats and human beings may 
play a considerable part in the dissemination of this disease. 

1 J. Hyg., Cambridge, 1906, VI, 530-535; 1907, VII, 373. 

2 Watkins-Pitchford, Rep. of Bacteriologist, Pietermaritzburg, Natal, 
1903 [Rep. on Plague, 31]. 

3 Gotschlich, Kolle u. Wassermann, Handbuch, Jena [etc.], 1904, 
IV 1 , 69. 

4 Martin, Ann. de l'lnst. Pasteur, Par., 1900. 

5 Gotschlich, Ztschr. f.Hyg. Infectionskrankh.,Leipz., 1899, XXXII, 
402. 

8 Gaffky, Klin. Jahrb., Jena, 1908, XIX, 491. 



CARRIERS AND MISSED CASES 43 

Bacillary Dysentery. — There are two forms of dysentery, 
one caused by a bacillus, the other by an ameba. Collins 1 and 
Goodwin 2 have studied the occurrence of the bacillus in well 
persons. According to Collins, Flexner, Wollstein and others 
failed to find it in healthy persons. Duval 3 found it in 
2 instances, and Charlton and Jehle 4 in 2 of 10 cases exam- 
ined. Collins found it in 2 of 30 normal persons, and in 1 
three weeks after an attack of dysentery, and in another child 
who had had a few mucous stools. Goodwin found the Flex- 
ner-Manila type of the bacillus in 1 of 59 well persons exam- 
ined. Kruse 5 says that all types of the bacilli have been 
found in well persons and that these carriers are an important 
cause of the disease. Though carriers have fewer bacilli in 
their feces, which are also less in volume, they come in con- 
tact with a larger number of persons than do the sick. There 
are also many mild atypical cases. Kruse has found the 
bacilli in relapses after two years, 6 and says that Drigalski 
and Lentz have made similar observations. He also cites 
Ford as finding 10 carriers among 50 persons examined. In 
an asylum outbreak Heuser 7 found 3 carriers. Conradi, 8 
while studying a contact outbreak near Metz, found several 
carriers. Kuster 9 isolated bacilli from a carrier who had 
probably been excreting since an attack years before. Kruse 
cites Kriege as saying that about 4 of 36 cases of dysentery 
become chronic, but usually the infection lasts only 2 to 6 
weeks. Conradi found that in 4 of 27 cases the bacilli per- 
sisted up to the end of the fourth week, while in 11 cases they 

1 Collins, Rep. Dept. Health, City of New York, 1904, I, 428. 

2 Goodwin, Rep. Dept. Health, City of New York, 1904, I, 423. 
8 Duval, Studies from Rockefeller Inst., 1904, II, 42. 

4 Charlton and Jehle, Tr. Ass. Am. Physicians, 1904, XIX, 405. 

6 Kruse, Med. Press & Circ, 1908, LXXXV, 175. 
« Kruse, Klin. Jahrb., Jena, 1908, XIX, 529. 

7 Heuser, Deutsche med. Wchnschr., 1909, XXXV, 1694. 

8 Conradi, Festschrift v. Robert Koch, 1903, 555. 

8 Kuster, Munchen med. Wchnschr., 1908, LV, 1833. 



44 THE SOURCES AND MODES OF INFECTION 

disappeared by the middle of the second week. Shiga 1 says 
that the bacilli generally remain 1 or 2 weeks, and that 
perfectly normal persons sometimes harbor the germs. Ave- 
line, Boycott and McDonald 2 failed to find the bacillus in 27 
contacts in an asylum. 

Mediterranean Fever. — Mediterranean fever, like plague, 
appears to be a disease of the lower animals, only secondarily 
affecting man. The germ which is its cause may, like so 
many other pathogenic organisms, develop in the body with- 
out giving rise to symptoms. Goats appear to be the chief 
source of human infection. In 1905 there were 363 cases 
among the garrison at Malta, but in 1906, presumably owing 
to the cutting off of the supply of goat milk, there were only 
35 cases; 3 and in 1907 it was practically exterminated. 4 An 
interesting account is given of an outbreak of the disease on 
a steamship, among persons who drank the milk of a herd of 
goats that were being brought to America. The goats were 
not sick. Horrocks 6 shows that probably one or more ani- 
mals in every herd are excreting the germs in the milk and 
urine, and that 50 per cent give evidence by serum reaction 
that they are, or have been, infected. Other investigations 
show that as high as 10 per cent of milch goats have the germs 
in their milk, although they present no symptoms of the 
disease. Carriers are also common among human beings. 
Shaw 7 found that 10 of 525 well persons were excreting the 
germs in the urine. 

Meningococcus in Nose. — While the germ of epidemic 
cerebro-spinal meningitis {Micrococais meningitidis) has been 

1 Shiga, Philippine J. Sc, Manila, 1906, I, 485. 

2 Aveline, Boycott and McDonald, J. Hyg., Cambridge, 1908, VIII, 
309. 

3 Hewlett, Practitioner (Lond.), 1908, LXXX, 222. 

4 Bruce, Nature, Lond., 1908, LXXVIII, 39. 

5 U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 41, 
203. 

6 Horrocks, Rep. of Commission of Roy. Soc, 1905-6, Pts. Ill, IV. 

7 Shaw, J. Roy. Army Med. Corps, Lond., 1906, VI, 638. 



CARRIERS AND MISSED CASES 45 

known for many years, it is only very recently that any ex- 
planation has been forthcoming as to the mode of infection. 
The finding of the organism in the nose of patients suggests 
the possibility that infection may pass to the brain from this 
point. It is theoretically possible for infection to take place 
through the cribriform plate of the ethmoid bone, or, as sug- 
gested by Westenhoeffer, 1 by the lymphatics from the pha- 
ryngeal tonsils, or as some think, by absorption from the 
alimentary canal and passage through the lymph channels or 
the general circulation. The organism is certainly found in 
the blood in a considerable number of cases. 2 What the exact 
route to the brain is, however, has not yet been determined. 

That the germ of this disease is found in the nose of the 
sick is now generally recognized, though considerable doubt 
has been thrown on the accuracy of some of the earlier obser- 
vations, as this organism is not readily distinguished from 
the cocci frequently found in the normal nose. Culture and 
agglutination tests are now recognized as the only valid 
methods of differentiation. Among those who have certainly 
isolated it in a considerable number of instances from the 
nasal mucous membrane of cerebro-spinal meningitis cases 
may be mentioned Dunham, 3 Weichselbaum and Gohn, 4 Lin- 
gelsheim, Goodwin and von Sholly 6 and others. 

Causes Rhinitis. — That this micrococcus is frequently found 
in the nose of contacts, and other persons showing no symp- 
toms of the disease, is now well established. An interesting 
case is that of Kiefer, 7 who while working with a culture in 
the laboratory developed a severe rhinitis and succeeded in 

1 Westenhoeffer, Bed. klin. Wchnschr., 1905, XLII, 737. 

2 Birnie and Smith, Am. J. M. Sc., Phila., 1907, CXXXIV, 582, and 
Simon, J. Am. M. Ass., Chicago, 1907, XLVIII, 1938. 

3 Dunham, J. Infect. Dis., Chicago, 1906 [Suppl. No. 2], 10. 

4 Weichselbaum and Gohn, Wien. klin. Wchnschr., 1905, XVIII, 625. 

5 Lingelsheim, Klin. Jahrb., Jena, 1906, XV, 373. 

6 Goodwin and von Sholly, J. Infect. Dis., Chicago, 1906 [Suppl. 
No. 2], 21. 

7 Kiefer, Berl. klin. Wchnschr., 1906, XXXIII, 628. 



46 THE SOURCES AND MODES OF INFECTION 

recovering the micrococcus from his nose. A similar case was 
reported to me by P. E. Rauschenbach, at the time working 
in a hospital at Newark. Ford 1 also had a case of this kind. 
Meningococcus in Contacts. — Among those who have 
found the organism in well persons may be mentioned Weich- 
selbaum and Gohn, 2 who obtained it in 3 of 24 persons exam- 
ined. Ostermann 3 found it in 17 of 24 contacts in Breslau, 
but his methods of employing the agglutination test have 
been called in question. One well child in whose nose the 
germs were found was taken sick three days later and died 
the next day. Many of the carriers had pharyngitis and 
rhinitis. Of 49 children in schools where these carriers at- 
tended, 2 showed the meningococcus, and one of these had 
been playing with a carrier. Ostermann failed to find it in 
50 persons who had not come in contact with cerebro-spinal 
cases. Goodwin and von Sholly, in New York, obtained it 
in 5 of 45 contacts, and a similar coccus which did not agglu- 
tinate, in 2 of 55 medical students not contacts. Bolduan 4 
found the organism in 10 per cent of 150 contacts. Lingels- 
heim, 5 during an extensive outbreak in Beulen, Prussia, found 
the organism in the nose of 26, or 9 per cent of 289 contacts. 
Later he found it in 4 of 56 school children, but all 4 came from 
families where there had been cases of the disease. In 2 of 
the 4 cases no agglutination test was applied. In the cases 
of the disease examined by Lingelsheim the micrococcus dis- 
appeared by the fifth day in 66 per cent, and by the sixth to 
tenth day in 24 per cent. In 4.39 per cent of the cases it per- 
sisted over three weeks, and in 1 case it was found three 
months from the beginning of the attack. 

1 Quoted by Councilman, J. Am. M. Ass., 1905, XLIV, 999. 

2 Weichselbaum and Gohn, Wien. klin. Wchnschr., 1905, XVIII, 
625. 

3 Ostermann, Deutsche med. Wchnschr., 1906, XXXII, 414. 

4 Bolduan, Med. Times, N. Y., 1908, XXXVI, 193. 

5 Lingelsheim, Deutsche med. Wchnschr., 1905, XXXI, 1017, 1217; 
Klin. Jahrb., Jena, 1908, XIX, 519. 



CARRIERS AND MISSED CASES 



47 



Infection in the Family. — Bruns and Hohn 1 found that the 
proportion of carriers decreased as the outbreak decreased. 
This is shown in the following table: 



March 
April . . 
May. . 
June . . 
July . . 
August 



Reported 
Cases. 


No. of 
Families 


No. of Well 

Persons 
Examined. 


No. of 
Carriers. 


148 


7 


23 


14 


278 


39 


135 


67 


327 


42 


172 


81 


188 


23 


93 


34 


146 


21 


67 


18 


68 


22 


119 


10 



Per cent of 
Carriers. 



61 
50 
47 
36 

27 
8.5 



They found that of the fathers in these families 60 of 113 
carried the germs; of the mothers, 39 of 114; of children in the 
families, 118 of 360; and of other members of the families 
7 of 22 were carriers. 

Persistence of Infection. — Bruns and Hohn give for the 
duration of the infection the following: 



For 8 days 28 cases 

2 weeks 18 cases 

3 weeks 13 cases 

4 weeks 10 cases 



For 5 weeks 4 

6 weeks 3 cases 

7 weeks 3 cases 

8 weeks 1 case 



Selter, in Bonn, 2 has observed a very much longer persist- 
ence of the infection. In the case of a mother and daughter 
who recovered from the disease, the cocci persisted from 
February 3 to June 4. The father in this family, who 
had not been sick, yielded positive findings in May, June, 
July and August, and had in all probability been infective 
for seven months. In another family where the disease ap- 
peared, the 6 well persons were carriers at one time or 
another from February 18 to June 5, during which period 

1 Bruns and Hohn, Klin. Jahrb., Jena, 1907-08, XVIII, 285. 
1 Selter, Klin. Jahrb., Jena, 1908-09, XX, 457. 



48 THE SOURCES AND MODES OF INFECTION 

they were examined twelve times. Sometimes the examina- 
tions were positive and sometimes negative, which is just 
what occurs in the examination of typhoid and diphtheria 
carriers. This apparent intermittency may be due in part 
to faulty technique, and in part to the temporary absence 
of the bacteria. In the 69 examinations of the family 
above referred to, 49 were positive and 20 negative. Selter 
could find no difference between the cocci found in the 
sick and in the carriers, but he was not able to trace a 
case of sickness to any of his known carriers. Kirchner, 1 
in Hamburg, found 22, or 9.7 per cent, carriers, out of 237 well 
members of infected families, but in 3 families all the mem- 
bers were carriers, and in 10 other families 75 per cent were. 
Most of these were adults. In two instances the infection 
persisted 44 and 66 days respectively. Vagedes 2 reports 3 
cases in barracks at Charlottenburg. Of 58 hospital attend- 
ants, etc., there, 4 were carriers, and of 593 of the soldiers 10 
only were carriers. On a second examination five days later 
1 only was found, and nineteen days later none. By the iso- 
lation of carriers the disease was " stamped out/' but it will 
be noticed that the infection was not widely diffused before it 
was recognized. Bochalli, 3 in certain barracks where the 
disease prevailed, found 10 of 16 roommates of the sick, or 
62 per cent, to be carriers. Of 485 in other companies, 42, or 
8.6 per cent, were infected. Usually the germs quickly dis- 
appeared, but in one case they persisted for four and a half 
months. In another instance a nurse, going to a district 
where there was no meningitis, was attacked about one month 
later. Similar observations have been made in several places 
during the recent outbreak in Scotland. Buchanan, 4 in Glas- 
gow, found the micrococcus in 81, or 26.3 per cent of 308 con- 

1 Kirchner, Klin. Jahrb., Jena, 1908, XIX, 473. 

2 Vagedes, Deutsche mil.-arztl. Ztschr., Berl., 1907, XXIII, 647. 

3 Bochalli, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1908, LXI, 



454. 



Buchanan, San. Rec, Lond., 1907 n. s., XI, 245. 



CARRIERS AND MISSED CASES 49 

tacts in 74 families. Most of them were over fifteen years of 
age. In 14 families he obtained it from more than one 
person, in 2 instances from five. In 4 instances it was 
found in the nose two years, one year, one year, and three 
months, respectively, after an attack. He quotes Arbuckle, 
medical officer j}f health of Partick, as finding 23.1 per cent 
of 230 contacts infected. In Leith, Fraser and Comrie 1 
found it in 10, or 14 per cent, of 69 contacts. Of these 5 were 
adults whose children were sick, and all of whom had worked 
on a ship in the air of whose engine room meningococci were 
found. Bethge, 2 immediately after the appearance of the 
first case in a certain institution, found that of 187 persons 
66 were carriers. 

Found only in Those near Sick. — The micrococcus which 
is the cause of this disease, while frequently noted in contacts, 
is rarely found in those not exposed to the disease. Oster- 
mann, when there were no cases about, failed to find the germ 
in 50 children and in many adults. Bolduan did not find it 
in 150. Kolle and Wassermann 3 recovered the germs from 
2 of 114 persons, but one had been in contact with the disease, 
and the other shortly became sick. Bochalli found none in 
40 men in a non-infected regiment, Lingelsheim 4 none in 
129 persons otherwise sick, and none in 184 non-exposed chil- 
dren, and he cites Droba and Kucera as finding none among 
210 children living where there was no meningitis. In 23 per- 
sons not exposed to the disease and examined by Fraser and 
Comrie none of these organisms were found. Arkwright 5 
failed to find them in 54 well persons, and Flexner 6 could 
find none in 50 persons in Philadelphia at a time when the 
disease was not present in the city. 

1 Fraser and Comrie, Scot. M. & S. J., Edinb., 1907, XXI, 18. 

2 Bethge, Deutsche med. Wchnschr., 1910, XXXV, 66. 

3 Kolle and Wassermann, Klin. Jahrb., Jena., 1906, XV, 507. 

4 Lingelsheim, Klin. Jahrb., Jena, 1906, XV, 373. 
6 Arkwright, J. Hyg., Cambridge, 1907, VII, 145. 
6 Flexner, J. Exper. M., N. Y., 1907, IX, 105. 



50 THE SOURCES AND MODES OF INFECTION 

As Lingelsheim says, it appears that the nearer we approach 
cases of the disease the more numerous carriers are, and the 
more extensive the outbreak the more numerous they are. 
Adults are more commonly infected than children. Fliigge 
thinks that carriers are ten to twenty times as numerous as 
cases, and that is doubtless true. 

Infection by Carriers. That carriers are the chief source 
of the disease is the opinion of those Germans who have lately 
had experience in severe outbreaks, and it is shared by the 
Scotch health officers. Lingelsheim says that there is no 
bacteriological or epidemiological evidence to show that the 
sick are more dangerous than the well, otherwise the cases 
would occur in groups. On the contrary the carriers mingling 
freely with the public are the most dangerous. Jehle 1 states 
that 23 cases occurred in children in the families of miners. 
None of the miners were sick, but when they were transferred 
to another mine, children there soon began to develop the 
disease. Their parents were doubtless carriers. Meyer 2 
reports an instance where carriers gave rise to three cases. 
At Leith, Buchanan 3 says that the first few cases could be 
traced to carriers, and Thomson 4 makes a similar statement 
regarding the early cases in Lanarkshire. Flatten 5 gives the 
details of numerous instances of the transmission of the dis- 
ease by well persons. 

Carriers explain Spread of Disease. — Previous to the dis- 
covery of the presence of the specific organism of cerebro- 
spinal meningitis in the nose, and particularly in the nose of 
contacts, the mode of extension of the disease was a mystery. 
Though certainly an infectious disease, and appearing in epi- 
demics, often quite severe, it was apparently only slightly if 

1 Jehle, cited by Warrington, J. Roy. San. Inst., Lond., 1907, XV, 656. 

2 Meyer, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1909, 
XLIX, 305. 

3 Buchanan, Brit. M. J., Lond., 1907, II, 852. 

4 Thomson, Med. Press & Circ, Lond., 1908, n. s., LXXXVI, 344. 
6 Flatten, Klin. Jahrb., Jena, 1906, XV, 265. 



CARRIERS AND MISSED CASES 



51 



at all contagious. Personally, out of over a hundred cases, I 
have only twice seen two cases in the same family, and have, 
except in those instances, never been able to trace connection 
between any two cases. Cases are frequently treated in con- 
siderable numbers in general hospitals all over the world, and 
infection of others has rarely, if ever, taken place. In New 
York a greater degree of contagiousness has been noted than 
in most places. 1 Of 1500 consecutive cases, 112, or 7 per cent, 
were secondary cases in the family. It is said that when more 
than one case occurs in a family they all are usually taken sick 
at about the same time, 2 but this was not so in New York. 
The following shows the date at which the secondary cases 
appeared in that city: 



Where First Cases 
Hospi 


were removed to 
tal. 


Where First Case remained at Home 


No. of Secondary 
Cases. 


Interval. 


No. of Secondary 
Cases. 


Interval. 


14 


1-7 days 


3 


1 day 


5 


1-2 weeks 


4 


2 days 


4 


2-3 " 


1 


3 " 


3 


3-4 " 


1 


5 " 


2 


4-5 " 


1 . 


6 " 


3 


5-6 " 


4 


7 " 


2 


7-8 " 


1 


9 " 


1 


3 mos. 


1 


11 " 


34 




1 


21 " 






1 


30 " 






18 





The 34 cases which developed after the removal of 
the primary case to the hospital indicate either that the 
germ of the disease remained in the house, on fomites, which 
is highly improbable, as its powers of resistance are extremely 

1 Am. Pub. Health Ass. Rep., 1905, XXXI, 359. 

" Bolduan and Goodwin, Med. News, N. Y., 1905, LXXXVII, 1222. 



52 



THE SOURCES AND MODES OF INFECTION 



slight, or that unrecognized carriers, persons with the coccus 
growing in the nose, remained behind, a supposition which 
is entirely in accord with bacteriological findings. In Glas- 
gow, 1 of 194 cases, 7, or 4.1 per cent, were secondary cases in 
the family. Some of these occurred after disinfection. It is 
not unlikely that the more extensive the outbreak the more 
numerous will be the " secondary " cases in the family. In 
Oppeln, where there was a very severe outbreak, Flatten 2 
found the number of secondary cases as follows in successive 
months of the outbreak: 





No. of Families. 


No. of Cases. 


January 

February 

March 


71 
143 
257 
310 
349 
374 


79 
163 
296 
368 
414 
439 


April 

May 


June • 



If, as appears, the meningococcus is frequently found in 
the nose of sick persons and of contacts, the mode of exten- 
sion of the disease becomes apparent. Observations indicate 
that a very considerable number of persons who come in con- 
tact with cases of this disease carry the organism on their 
mucous membrane. Yet very few of these persons ever be- 
come sick. It appears that the development of the cerebro- 
spinal symptoms, that is the disease as we know it, is really 
a rather unusual accident of a not uncommon harmless infec- 
tion of the nasal passage. We can therefore understand how 
the disease, though apparently showing little contagiousness, 
is nevertheless a strictly contagious disease. It extends almost 
entirely through the agency of carriers. Sometimes, as was 
previously stated, these carriers can be discovered, particu- 

1 Rep. Med. Off. Health, Glasgow, 1906, 89. 
* Flatten, Klin. Jahrb., Jena, 1906, XV, 228. 



CARRIERS AND MISSED CASES 53 

larly early in an outbreak. The appearance of cases in dif- 
ferent localities in a community, and at varying intervals, is 
readily explained by, and is almost a proof of, the existence 
of a considerable number of undiscovered carriers. 

Meningitis an Accident of Infection. — The growth of the 
germs in the nose cannot properly be considered the " incu- 
bation" of the disease. Inoculation experiments 1 indicate 
that the nervous symptoms develop in a very few hours after 
the specific bacteria are injected into the meninges. There 
is much evidence, as given above, to show that the germs may 
grow on the surface of the nasal mucous membrane for days, 
weeks and perhaps months, but when they once gain access 
to the meninges the symptoms of the disease speedily 
develop. 

Meningitis also occurs as a result of infection by the pneu- 
mococcus. The disease thus caused is not essentially different 
from the epidemic form. The number of well carriers of the 
pneumococcus is enormously greater, and is much more con- 
stant than is the number of carriers of the meningococcus, 
and the chance of the former invading the meninges and caus- 
ing sickness is small, very much less than the chance of the 
latter doing so. In either case it may be considered an unfor- 
tunate accident of a usually benign infection. 

Inutility of Isolation of Meningitis. — If these views are 
correct, little can be done by means of isolation to prevent 
the spread of the disease. When an outbreak occurs, there 
is certain to be a large number of carriers that cannot be 
found or isolated. To isolate the sick, and even those in 
immediate contact with the sick, will probably never make 
any appreciable difference in the progress of the disease, that 
is if the findings of to-day are confirmed by more extended 
observations. By the time several cases have developed in 
a community, there will probably usually be a considerable 
number of carriers who cannot be found. Stringent isola- 

1 Lingelsheim, Deutsche med. Wchnschr., 1905, XXXI, 1017, 1217; 
Flexner, J. Exper. M., N. Y., 1907, IX, 142. 



54 THE SOURCES AND MODES OF INFECTION 

tion of the families of known cases will accomplish little, and 
will work much hardship and injustice. 

Diphtheria Bacilli in Well Persons. — Loeffler 1 himself in 
1884 found diphtheria bacilli in a person who was not sick, 
and in 1889 Roux and Yersin 2 called attention to the per- 
sistence of diphtheria bacilli on the mucous membranes of 
convalescents, and their observations were at intervals sub- 
stantiated by others. In 1894 Park and Beebe 3 examined the 
throats of 330 healthy persons who had not, so far as known, 
been in contact with diphtheria cases, and found diphtheria 
bacilli in 24, or 7.3 per cent, but of these only 8, or 2.4 per cent, 
of the 330 were virulent. These authors minimized the dan- 
ger to be apprehended from these carriers, and although for 
some time similar observations were reported, they were gen- 
erally, and are even now by many, considered of little impor- 
tance. It seems to me otherwise, and therefore a considerable 
number of these observations are here summarized. Miiller 4 
examined in routine 92 children sick with diseases other than 
diphtheria, in Heubner's clinic, and reported that 12, or 13 
per cent, were infected with diphtheria, but only 6 of the 12 
were tested on guinea pigs. Later 18 children in the same 
institution, who had negative cultures on admission, were 
found to harbor the bacilli. Kober 5 in Breslau found that 
of 600 school children 2.5 per cent were carriers of diphtheria 
bacilli, but in only 0.83 per cent of the 600 were they virulent. 
At Baltimore, 6 in 1899, during an exceptional prevalence of 
diphtheria in a number of schools, cultures were taken from 
4068 pupils apparently well, and of these 157, or 3.8 per cent, 

1 Loeffler, The Bacteriology of Diphtheria, Nuttall and Graham- 
Smith, Cambridge, 1908, 31. 

2 Roux and Yersin, Ann. de l'Inst. Pasteur, 1890, IV, 385. 

3 Park and Beebe, Med. Rec., N. Y., 1894, XLVI, 385; Sci. Bull. 1, 
Dept. Health N. Y. City, 1895. 

4 Miiller, Jahrb. f. Kinderh., 1896, XLIII, 54. 

6 Kober, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXXI, 
433. 

Baltimore, Rep. Com. of Health, 1899, 96; 1900, 85. 



CARRIERS AND MISSED CASES 55 

showed diphtheria bacilli. The next year, of 351 examined, 
23, or 6.6 per cent, were positive. 

Varieties of Bacilli found. — Reports of the finding of diph- 
theria bacilli in well persons would have more value if it were 
made clear what was meant by the term diphtheria bacilli. 
The bacillus varies greatly in form, and those who have 
studied it most carefully are by no means agreed as to what 
should or should not be properly so called. Fortunately 
Wesbrook's classification of all these varieties, both admitted 
and questioned, renders it possible to interpret properly the 
reports of all who will take the trouble to use his nomencla- 
ture, and it is to be regretted that more do not use it. Again, 
diphtheria bacilli are quite as frequently found in the nose as 
in the throat, but few observers state whether the cultures 
were taken from throat or nose or both. For the purpose of 
securing definite data from a large number of cases, a col- 
lective investigation was undertaken by the Massachusetts 
Association of Boards of Health. 1 The number of persons 
examined was 4250 in different parts of the United States. 
Most of them had probably not been directly exposed to diph- 
theria except in Minnesota, where most of the cultures were 
taken from schools and institutions where there had recently 
been cases of the disease. The majority of the persons ex- 
amined were adults, and cultures were taken from both throat 
and nose. Of all persons examined, 2.89 per cent had "granu- 
lar " forms of diphtheria bacilli, i.e., those showing polar 
staining with methylene blue. If " barred " and other aber- 
rant types are to be considered as diphtheria bacilli, as they 
are by some, the number of cultures to be reported positive 
would have been more than doubled. Referring only to the 
typical granular types, 1.46 per cent of all persons showed 
throat infection (either with or without concurrent nose infec- 
tion) and 2.07 per cent showed nose infection (either with or 
without concurrent throat infection). In the different cities 
the percentage of infected persons varied from 0.43 in Provi- 

1 J. Mass. Ass. Bds. Health, Bost., 1902, XII, 74. 



56 THE SOURCES AND MODES OF INFECTION 

dence, where particular care was taken to avoid contacts, 
most of the cultures being taken from schools where there 
had been no diphtheria for at least two years, to 3.66 in the 
Willard State Hospital, and 6.03 in Minnesota, in both of 
which localities there had recently been diphtheria in the 
institutions examined. There were 47 tests for virulence, of 
which 8, or 17 per cent, were positive. Recently cultures were 
taken from school children in Brighton (Boston) by Slack. 1 
Of over 4000 children examined by throat and nose culture on 
two occasions, 1.93 per cent showed diphtheria bacilli. Of 
these 8 were tested for virulence, of which all proved to be non- 
virulent. Most of these children were excluded from school 
until free from bacilli, but all of them had, of course, been 
carrying bacilli in school for a longer or shorter period. No 
case of clinical diphtheria was traced to any of these carriers, 
either in school or out of school. These facts have been ad- 
vanced as evidence that the danger from such carriers is a 
negligible factor in contrast with the danger from conva- 
lescents whose bacilli are usually virulent. But in Providence 
in 1908, 73 convalescents carrying diphtheria bacilli were 
admitted to school, and it is not known that they were in any 
instance the source of new cases in the school, and in all but 
two or three instances it is certain that they were not. 
Forbes 2 cites Meikle as reporting 27 carriers discharged from 
the hospital without any return case. These facts merely in- 
dicate that the amount of danger from a single focus of 
infection is much less than is generally believed. 

Value of Bacteriological Findings. — Neumann 3 could not 
find any diphtheria bacilli in 111 perfectly normal throats 
and noses, but did find them in 8 of 95 cases suffering from 
catarrhal inflammation of the mucous surfaces. He does not 
think that they are found in normal throats, but certainly 
all who have had any experience in taking cultures have seen 



Slack, Arms, Wade and Blanchard, J. Am. M. Ass., 1910, LIV, 951. 

Forbes, Brit. M. J., 1909, II, 522. 

Neumann, Ztschr.f.Hyg.u. Infectionskrankh., Leipz., 1902, XL, 33. 



CARRIERS AND MISSED CASES 57 

numberless cases where diphtheria bacilli were found in 
throats which, so far as appearances go, were perfectly nor- 
mal. When diphtheria bacilli are found on a reddened or 
slightly inflamed mucous surface, the abnormal condition 
may not in every individual case be due to their presence, for 
certainly " catarrhal " inflammations of nose and throat, due 
to other causes than the presence of diphtheria bacilli, are 
extremely common. The evidence is that at present, in cities, 
from 1 to 2 per cent of the population are infected with 
diphtheria bacilli. The presence of diphtheria bacilli in an 
inflamed throat may be, then, in 1 or 2 per cent of the find- 
ings merely a coincidence. It is safe to assume that in all 
but 1 or 2 per cent the presence of diphtheria bacilli stands 
in causative relation to the inflammation of the surface on 
which they are found. 

Diphtheria Bacilli in Children. — In Bristol, Heaven 1 ex- 
amined 704 children (throat and nose) connected with schools 
where there had been considerable diphtheria, and found 
diphtheria bacilli in 24, or 3.4 per cent. Of 758 cultures taken 
from schools in London where there had been occasional cases 
of diphtheria, 58, or 7.6 per cent, showed the bacilli. 2 Pen- 
nington 3 examined 375 well children in Philadelphia schools, 
in some of which there had been more or less diphtheria, and 
of 37 positive cultures from these, 24 were more or less viru- 
lent. Of 125 pupils from four other schools 10.4 per cent gave 
positive cultures, about half of which were virulent. But 
Pennington found that of 25 cultures from convalescents 22 
were virulent. In the city of Mexico, of 300 school children 
10, or 3.3 per cent, showed diphtheria bacilli. 4 Von Sholly :) 
examined 1000 tenement-house children in New York, taking 
cultures only from those whose throats appeared normal. The 

1 Heaven, Pub. Health, Lond., 1902-03, XV, 516. 

2 Rep. Med. Off. Health, Lond., 1904, Appendix III, 25. 

3 Pennington, J. Infect. Dis., Chicago, 1907, IV, 36 

4 Fabela, Rep. Am. Pub. Health Ass., 1906, XXXII, Pt. 2, 199. 

5 Von Sholly, J. Infect. Dis., Chicago, 1907, IV, 337. 



58 THE SOURCES AND MODES OF INFECTION 

children for the most part were those brought to hospitals 
and dispensaries for treatment, but all cases were excluded 
which had any suggestion of sore throat, nasal discharge, 
etc. Of these 1000 cases 5.6 per cent showed diphtheria- 
like organisms, of which, however, only 1.8 per cent (of 
the 1000 cases) proved to be virulent. In 50 of the cases 
nose cultures also were taken, and one of these proved to 
have virulent bacilli. During a very severe outbreak of diph- 
theria in Christiania, Ustvedt 1 examined 4277 school children, 
and found diphtheria bacilli in 191, or 4.5 per cent. Of these, 
10 afterwards developed diphtheria. Of 7 cultures tested for 
virulence 4 were positive. In one school in which the per- 
centage of positive cultures was 9.2 during the outbreak, it 
was 3.2 some months later. In a school in the country where 
there had been no diphtheria for years, no bacilli were iso- 
lated from 86 pupils. Ruediger 2 found diphtheria bacilli in 
3 of 51 normal throats. Gross 3 took two throat and nose 
cultures from 314 children (without diphtheria) on admission 
to the Children's Hospital in Boston, and isolated diphtheria 
bacilli from 26, or 7.9 per cent. Five were tested for viru- 
lence, 4 of which were positive. Hewlett and Murray 4 
found that 58, or 15 per cent, of 385 children on admission to 
the Victoria Hospital for Children in London, were diphtheria 
carriers, and that in children under two years of age the per- 
centage was 21. Cobbett 5 at Cambridge reported diphtheria 
bacilli in 2.9 per cent of 650 well persons, many of whom were 
contacts. Some had mild sore throat. 

Diphtheria Bacilli in Scarlet Fever. — While the presence 
of diphtheria bacilli in scarlet fever cases sheds little light 
on their prevalence in normal throats, it is of much interest 

1 Ustvedt, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1906, LIV, 
147. 

2 Ruediger, J. Am. M. Ass., Chicago, 1906, XLVII, 1173. 
" Gross, Univ. M. Mag., Phila., 1896-7, IX, 45. 

4 Hewlett and Murray, Brit. M. J., Lond., 1901, I, 1474. 
6 Cobbett, J. Hyg., Cambridge, 1901, I, 242. 



CARRIERS AND MISSED CASES 59 

from an epidemiological standpoint. The exudation which 
frequently covers the tonsils in scarlet fever is often mistaken 
clinically for a sign of diphtheria, and such cases are, before the 
appearance of the eruption, often reported as diphtheria, so 
that there is a popular impression among physicians that the 
two diseases are frequently combined, and that the presence 
of scarlet fever predisposes to diphtheria. While bacteriolog- 
ical examinations tend to show that diphtheria infection on 
scarlet fever is not so common as is often assumed, and that 
many cases reported as a combination of the two diseases are 
not really such, yet diphtheria bacilli are frequently found in 
cases of scarlet fever, more frequently than they are found 
in the general public from whom the scarlet fever cases come. 
In Providence during the past four years cultures have 
been taken from 92 scarlet fever cases in their homes, of 
which 6, or 6.5 per cent, were positive. Of 245 cultures in the 
hospital, 26, or 10.6 per cent, were positive. During the pre- 
ceding three years 116 cultures were taken, but it was not 
recorded whether they were from hospital or home cases, and 
of these, 5, or 4.3 per cent, were positive. The excessive per- 
centage of positive findings in the hospital was due to infec- 
tion after admission. Both throat and nose cultures were 
taken in nearly every case. In the Western Fever Hospital 
of London, 1 of 1019 throat swabs taken from the same num- 
ber of scarlet fever patients on admission, 7.86 per cent were 
positive; at another hospital 5.41 per cent of 203 cases, and 
at another 6.8 per cent of 87 cases. Of the 939 cases at the 
Western Hospital which did not have diphtheria bacilli on 
admission, 6 later developed diphtheria, ranging from the ninth 
to the fiftieth day after admission, and 28 more acquired 
diphtheria bacilli without being sick. Of the 80 cases that 
entered infected, 4 developed clinical diphtheria on the 
fourth, fifth, seventh and thirty-first days. Soerensen 2 found 
that of 1547 scarlet fever cases examined on admission, 38, or 

1 Cumpston, J. Hyg., Cambridge, 1907, VII, 598. 

2 Soerensen, Ztschr. f. Hyg. u. Infectionskrankh., 1898, XXIX, 250. 



60 THE SOURCES AND MODES OF INFECTION 

2.5 per cent, carried diphtheria bacilli. During a service of two 
years 32 cases of diphtheria occurred in the scarlet fever wards 
among about 1500 patients, and 208 others were found to be 
infected but not sick. Ruediger 1 found diphtheria in 4 of 75 
scarlet fever throats, or 5.3 per cent. Garratt and Wash- 
bourn 2 found diphtheria germs in 8, or 1.2 per cent, of 666 
scarlet fever cases. In Croydon, 3 37, or 17.3 per cent, of 213 
cases of scarlet fever were shown to be infected with diph- 
theria bacilli on admission to the hospital. In Brighton, 4 in 
1905, 33, or 25.9 per cent, of 166 cases of scarlet fever had 
diphtheria bacilli present, and all but one were infected on 
admission; in 1907, 21 of 340 were infected. In Bristol, 5 of 
202 scarlet fever patients in the hospital in 1904, 75 per cent 
had positive cultures on admission. In 1905, of 476 cases, 21 , 
or 4.4 per cent, were positive, besides 3 others which showed 
symptoms of the disease. In Philadelphia, of 700 scarlet 
fever admissions, 11 per cent showed diphtheria bacilli. 

Percentage of Diphtheria Carriers. — The evidence thus 
far adduced tends to show that diphtheria bacilli are quite 
widely distributed in the urban population of Europe and 
America. Perhaps on the average 1 or 2 per cent harbor the 
germs of this disease in mouth or nose; but observations also 
indicate that the less diphtheria there is in a community, 
and the farther removed the persons examined are from cases 
of the disease, the less likely they are to be infected. Thus 
in Christiania during an outbreak, 9.2 per cent of the pupils 
in a certain school were infected, while some months later 
the ratio was only 3.2. The Massachusetts Association of 
Boards of Health report an infection of 6.03 per cent of the 
school children recently exposed to diphtheria in Minneapolis, 
while in schools in Providence where there had been no diph- 

1 Ruediger, J. Am. M. Ass., Chicago, 1906, XLVII, 1173. 

2 Garratt and Washbourn, Brit. M. J., Lond., 1899, I, 893. 

3 Rep. Med. Off. Health, Croydon, 1904, 68. 

4 Rep. Med. Off. Health, Brighton, 1905, 42; 1907, 22. 
6 Rep. Med. Off. Health, Bristol, 1904, 100; 1905, 71. 



CARRIERS AXD MISSED CASES 



61 



theria for a long time the ratio was only about one-half of 
1 per cent. 

Percentage among Contacts. — There are numerous obser- 
vations made on persons brought more or less closely in con- 
tact with the sick, which show that under such conditions 

Percentage of Carriers in Diphtheria Families, Providence, 1897-1901. 



Ages. 


Persons ex- 
amined. 


Number of 
Carriers. 


Percentage 
of Carriers. 


Under 1 year .... 


119 


17 


14.2 


1 " 


112 


15 


13.3 


2 years 


97 


23 


23.7 


3 " 


112 


25 


22.3 


4 " 


116 


31 


26.7 


5 " 


120 


17 


14.1 


6 " 


137 


42 


30.6 


7 " 


130 


30 


23.1 


8 " 


119 


25 


21.0 


9 " 


113 


23 


20.3 


10 " 


139 


26 


18.7 


11 " 


79 


11 


13.9 


12 " 


127 


28 


22.0 


13 " 


86 


15 


17.4 


14 " 


88 


13 


14.7 


15 " 


70 


5 


7.1 


16 " 


64 


9 


14.0 


17 " 


57 


9 


15.7 


18 " 


57 


6 


10.5 


19 " 


45 


4 


8.8 


20 " 


34 


4 


11.7 


Adults 


2505 


277 


11.0 


Totals 


4526 


655 


14.4 





the number of carriers may be very high. For several years 
in Providence 1 cultures were taken from all the wage earners 
in the family at the time the case was reported, and from all 
the members of the family for release, that is, to determine 



Rep. Supt. Health, Providence, 1901, 44. 



62 THE SOURCES AND MODES OF INFECTION 

the end of isolation. Only throat cultures were taken. Of 
4526 such contacts examined 14.4 per cent were found to be 
infected. If nose as well as throat cultures had been taken, 
and if cultures had been taken from the whole family about 
midway in the course of the disease, I imagine the percentage 
would have been several times greater. The preceding table 
shows the percentage infected at different ages. The women 
in the family were infected very much oftener than the men. 
It was noticed that in about 10 per cent of the cases some 
well member of the family remained infected after the patient 
was entirely free from germs. In Glasgow, 1 of 2305 contacts 
in infected families 9.2 per cent were carriers. 

Percentage of Carriers in Infected Schools. — In a certain 
school in Minnesota, 2 of 263 well children, 129, or 49 per cent, 
were infected with the granular and barred types of the bacil- 
lus. In Bristol 3 during a school outbreak in 1907, of 190 
well children, 12.5 per cent were carriers. At the Willard Hos- 
pital for the Insane during an outbreak, of 1423 well persons, 
189, or 13 per cent, were carriers. At the State Hospital in 
California, 11.6 of 1115 persons were infected. 4 In Provi- 
dence during an outbreak of diphtheria in an infant asylum, 
of 175 children and adults, 116 or 66.2 per cent, proved to be 
infected at one time or another, but this was only after many 
repeated cultures extending over a period of some months. 
Many of them were persistent carriers, one of them remaining 
infected for twenty-two months- Crowley ° in a school out- 
break found 42 of 93 children infected, or 45 per cent. In 
Bermondsey, London, 6 the children in diphtheria families 
have a single throat culture taken, and of 597 children so 

1 Rep. Med. Off. Health, Glasgow, 1908, 71. 

2 Wesbrook, St. Paul M. J., St. Paul, Minn., 1900, II, 219 [p. 6 of 
reprint]. 

3 Rep. Med. Off. Health, Bristol, 1907, 51. 

4 Rep. Calif. St. Bd. Health, 1906-08, 201. 

5 Crowley, J. Roy. San. Inst., 1904-05, XXV, 807. 

6 Rep. Med. Off. Health, London, 1904, 31. 



CARRIERS AND MISSED CASES 63 

examined 64, or 10.8 per cent, were found to be infected. Of 
115 well children in an institution in Minneapolis, Corbet l 
found 29, or 25.2 per cent, infected. In several instances the 
bacilli presented atypical forms, but many of these were viru- 
lent. In a school in the same city, where there had been some 
diphtheria, he found that 20, or 14.3 per cent, of 140 cultures 
showed the presence of typical bacilli. 2 Ustvedt, 3 in Chris- 
tiania, found 17 per cent of contacts infected. In a school at 
Oakland, California, 4 25 per cent of the pupils were carriers. 
In Glasgow, 5 of 322 well members of diphtheria families 10.5 
per cent were infected. In the Duke of York's school, Lon- 
don, of 536 well pupils 117, or 20 per cent, showed diphtheria 
bacilli, and of these 10 later had diphtheria, while only one 
of the " free " boys developed it. Of 13 cultures from the 
well boys, 7 were virulent, though mildly so, but the bacilli 
from the sick also showed a low virulence. It is worthy of 
note that the disease recurred in this school for two or three 
years. 6 von Sholly 7 found bacilli in 20 of 202 contacts, or 
about 10 per cent, and of these 14 were virulent. Buchanan 8 
in Glasgow found that the bacilli were virulent in 66 per 
cent of 21 healthy carriers, and that bacilli recovered from 
56 cases of the disease proved virulent only in 74 per cent. 
Aaser 9 found 19 per cent of contacts in cavalry barracks in- 
fected, and 20 per cent of children in a scarlet fever ward. 
Hellstrbm 10 in Stockholm, of 786 soldiers who had been more 

1 Corbet, Rep. Com. Health, Minneapolis, 1905, 7. 

2 Rep. Com. Health, Minneapolis, 1903, 16. 

3 Ustvedt, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., 1906, LIV, 147. 
* Bull. Calif. St. Bd. Health, November, 1906. 

6 Rep. Med. Off. Health, Glasgow, 1906, 135. 

6 Arkwright, J. Hyg., Cambridge, 1908, VIII, 48 ; Rep. Med. Off. 
Health, Lond., 1906, 36. 

7 von Sholly, J. Infect. Dis., Chicago, 1907, IV, 337. 

8 Buchanan, Brit. M. J., Lond., 1909, II, 519. 

9 Aaser, Deutsche med. Wchnschr., 1895, XXI, 357. 

10 Hellstrom, cited by Kober, Ztschr. f. Hyg. u. Infectionskrankh., 
Leipz., 1899, XXXI, 433, and by Fibiger, Berl. klin. Wchnschr., 1897, 
XXXIV, 753. 



64 THE SOURCES AND MODES OF INFECTION 

or less in contact with diphtheria, found 151, or 19.2 per cent, 
infected. Goadby, 1 in 586 pupils in a school where there had 
recently been 21 diphtheria cases, found that 190, or 34.1 
per cent, were carriers, and he quotes Meade Bolton as finding 
45.5 per cent of 214 contacts infected. Of the children ex- 
amined by Goadby 262 had enlarged tonsils and 196 abnor- 
mal throats. In another school where there had been no 
reported cases, 18 of 100 were infected. 

Berry and Washbourn 2 report 17, or 11.9 per cent, of 
infected contacts in a school of 142 girls. Lister 3 found 48 
per cent of 125 contacts in Shadwell Hospital infected. 
Twenty-four of them had nasal discharge. Park and Beebe 4 
in a foundling asylum obtained virulent bacilli and one non- 
virulent form from 5 of 55 contacts. Fibiger, 5 during a school 
outbreak of diphtheria, recovered the bacilli in 22, or 16.4 per 
cent, of 134 children. Denny 6 found 11 per cent of 200 chil- 
dren infected, in a school where there had recently been 4 cases 
of diphtheria, and Graham-Smith, 7 10.4 per cent of 519 school 
children. Gabritschewsky 8 in the Russian military service 
found, during the prevalence of diphtheria, that 20 per cent 
of the well persons examined were carriers, and in a school 
in Moscow, at a time when there was much diphtheria, 21 of 
66 well children showed diphtheria bacilli. 

Atypical Diphtheria. — The old notion was, and I fear that 
very many physicians and not a few health officers so believe 
to-day, that diphtheria is a well defined disease with charac- 
teristic symptoms. They cannot imagine diphtheria without 

1 Goadby, Lancet, Lond., 1900, I, 236. 

2 Berry and Washbourn, Brit. M. J., Lond., 1900, I, 198. 

3 Lister, Brit. M. J., Lond., 1898, II, 1338. 

4 Park and Beebe, Med. Rec., N. Y., 1894, XLVI, 385. 

5 Fibiger, Berl. klin. Wchnschr., 1897, XXXIV, 753. 

6 Denny, Bost. M. & S. J., 1900, 515. 

7 Graham-Smith, J. Hyg., Cambridge, 1903, III, 216. 

8 Gabritschewsky, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1901, 
XXXVI, 45. 



CARRIERS AND MISSED CASES 65 

serious illness. There always have been, however, some acute 
clinicians who thought otherwise. Jacobi in New York was 
among the foremost. He recognized that the disease often 
presented a mild type and that diagnosis was impossible. 
He said in 1884: * 

"The symptoms are often but few. A little muscular pain 
and difficult deglutition are, perhaps, all that is complained 
of. Women will quietly bear it; men will go about their busi- 
ness. . . . There is as much diphtheria out of bed as in bed; 
nearly as much out of doors as indoors. Many a mild case 
is walking the streets for w^eeks without caring or thinking 
that some of his victims have been wept over before he was 
quite well himself. . . . Diphtheria is contagious. Severe 
forms may beget severe or mild forms. Mild cases may beget 
mild or severe cases." 

Under Jacobi's teaching I early learned to look for such 
mild cases, and I remember seeing an outbreak in a children's 
home during the early eighties, in which there were many 
very mild sore throats and walking cases. Mild diphtheria 
of this type does not usually come to the notice of a physician, 
and when it does is frequently not recognized. How fre- 
quent such cases are it is difficult to determine, but they must 
be very numerous. In a general hospital at Chelsea 2 (Lon- 
don), where there had been considerable trouble from out- 
breaks of diphtheria, it was determined to take cultures from 
all patients admitted who showed any symptoms of sore 
throat. Of 815 persons so examined 65, or 7.3 per cent, gave 
positive cultures. In New York City 3 the school inspectors 
were directed to take cultures from all children showing slight 
redness of the throat or hypertrophied tonsils. Of 11,451 
cultures 757, or 6.7 per cent, were positive. These children 
were not in any sense considered as ill, yet the percentage 

1 Quoted by Solis-Cohen, J. Am. M. Ass., Chicago, 1907, XLIX, 32. 

2 Parkes, Pub. Health, Lond., 1902-03, XV, 538. 

3 Letter from Dr. Cronin, X. Y. Bd. Health, Sept. 23, 1904. 



66 THE SOURCES AND MODES OF INFECTION 

infected is certainly much higher than would be looked for 
among the general school population. In Hartford x during 
the years 1900-1903 cultures were taken from 2038 mild sore 
throats seen in the schools. Of these, 591, or 29 per cent, were 
positive. These children might be said to have a decided sore 
throat, though they were all well enough to be in school. 
They were all excluded from school. During the same period 
there were reported in Hartford 1537 cases of diphtheria, so 
that the cases found in the manner described equaled one- 
third of the total cases. In Indianapolis, 2 at a time when 
there were 60 reported cases of diphtheria in the city, a dili- 
gent search for, and taking of cultures from, sore throats 
among the school children revealed the presence of 46 other 
cases. Every one knows how extremely common sore throat 
and tonsillitis are, and even if only a very small proportion, 
much less than 29 per cent, of these, are true diphtheria, the 
number in the aggregate must be very large. I think I am well 
within bounds when I assume that for every recognized case of 
diphtheria there is at least one sore throat which is also diph- 
theria though unrecognized. Judging from the proportion of 
mild cases in institution outbreaks, the proportion of unrec- 
ognized, mild, but yet clinical cases, must be much greater 
than that. Careful medical inspection often discovers that 
these missed cases have been the source of reported cases. 
For example, the Report on the Health of the City of Man- 
chester (England), 1906, gives a list of 29 cases caused in this 
way during that year. 

Rhinitis and Otitis. — Diphtheria sometimes assumes a 
chronic form with few symptoms. Indeed some, as Neumann, 
believe that long persistence of diphtheria bacilli in throat 
and nose is always accompanied by local disturbance. That 
such is often the case in the nose, and that subacute 
chronic rhinitis may be a form of diphtheria, and may give 
rise to typical pharyngeal cases, is generally recognized. 

1 Reps. Bd. Health, Hartford, 1900 to 1903. 

2 Rep. Dept. Pub. Health & Charities, Indianapolis, 1908, 8. 



CARRIERS AND MISSED CASES 67 

Park, 1 Abbott, 2 Ravenel, 3 Schaps, 4 Treitel and Koppel, 5 
DeStella, 6 Ballin 7 and many others report cases of chronic 
rhinitis due to the presence of the diphtheria bacillus. The 
middle ear sometimes suppurates in diphtheria, as it does in 
scarlet fever, though less frequently, and this discharge may 
remain virulent for long periods. 8 I happen to have such a 
case under observation at the present time. 

A Real Danger. — There can be no doubt, then, that mild 
and unrecognized cases of diphtheria are very common, that 
convalescents long harbor the bacilli, and that contacts and 
other carriers are very numerous; in fine, that these sources 
of infection far outnumber the cases of recognized sickness. 
But are these really sources of infection, or are they, as so 
many believe, an imaginary danger evolved in the brain of 
the laboratory worker ? It is well again to emphasize the 
fact that long before Klebs and Loeffler identified the bacillus 
of this disease a few able clinical observers like Jacobi be- 
lieved that evidence pointed clearly to the great danger of 
these unrecognized sources of infection. The bacteriologists 
have not raised the bugaboo of carrier infection, they have 
simply explained the facts which observing men have long 
recognized. 

Carriers cause Disease. — A little perusal of medical liter- 
ature will show that many cases are reported of what is 
apparently the distribution of diphtheria by carriers. 

Peck 9 reports an instance where a young man who was 

1 Park, Med. Rec, N. Y., 1892, XLII, 121. 

2 Abbott, Med. News, Phila., 1893, LXII, 505. 

3 Ravenel, Med. News, Phila., 1895, LXVI, 537. 

4 Schaps, Arch. f. Kinderh., Stuttg., 1905, XL, 80. 

6 Treitel and Koppel, Arch. f. Kinderh., Stuttg., 1895-96, XIX, 107. 

6 DeStella, Arch, internat. de laryngol. [etc.], Par., 1903, XVI, 970. 

7 Ballin, Jahrb. f. Kinderh., 1903, LVIII, 412. 

8 Newsholme, Rep. Med. Off. Health, Brighton, 1906, 13; Address at 
Victoria Univ., Manchester, March 9, 1904, 21. 

9 .Peck, Brit M. J.. Lond., 1895, I, 971. 



68 THE SOURCES AND MODES OF INFECTION 

perfectly well but was a carrier, probably gave diphtheria to 
another young man with whom he slept. 

In 1897 a mother whom I saw, stayed for a few days in a 
house on a neighboring street taking care of a diphtheria 
case. Soon after her return home her son was taken sick with 
diphtheria, and when cultures were taken from her throat she 
also was found to be infected. 1 In 1905 a child who was sent 
to the hospital for some surgical lesion developed scarlet 
fever and was removed to the scarlet-fever ward. Three days 
after his return home another child in the family was taken 
sick with diphtheria, and a few days later a culture taken 
from the first child was positive. 2 Wesbrook 3 reports: " Two 
always well children carrying bacilli sent home. Diphtheria 
broke out shortly after their arrival. No other source of 
infection discovered. One always well girl carrying diph- 
theria bacilli went to her home. Stepmother and children 
developed diphtheria within a few days. This family was 
practically isolated in the country." 

Hellstrom, 4 during a diphtheria outbreak in a cavalry regi- 
ment, noted two instances in which perfectly well soldiers 
who had diphtheria bacilli on their mucous membrane car- 
ried the disease to others. Aaser 5 reports a child with diph- 
theria germs taking the disease home from a scarlet-fever 
ward where there was a diphtheria outbreak. 

In 1906 at Birmingham 6 there was a milk outbreak of 
diphtheria of 13 cases due to infection of the milk by the 
milk handlers, who had diphtheria bacilli in their throats, but 
were not sick. As soon as they were isolated the outbreak 
ceased. Similar milk outbreaks caused by infected well per- 

1 Rep. Supt. Health, Prov., 1897, 21. 

2 Rep. Supt. Health, Prov., 1905, 32. 

3 Prelim. Rep. on Diphtheria in Well Persons, J. Mass. Ass. Bds. 
Health, Bost., 1901, XI, 10. 

4 Hellstrom, cited by Fibiger, Berl. klin. Wchnschr., 1897, XXXIV, 
753. 

5 Aaser, Deutsche med. Wchnschr., 1895, XXI, 357. 

6 Rep. Med. Off. Health, Birmingham, 1906, 40. 



CARRIERS AND MISSED CASES 69 

sons have been reported from Fitchburg, 1 Lowell, 2 Brookline, 3 
Montclair, N. J., 4 Oroville, Cal., 5 Australia 6 and other places. 

At the .Willard State Hospital 7 a watchman, who lived 
with his son-in-law in the village, who had diphtheria, was 
never sick but was a carrier. He played cards with two 
clerks, and they all drank from the same pitcher. The clerks, 
who had not been exposed to diphtheria, were a week later 
taken sick with the disease. Four other instances of infection 
by carriers occurred during the same outbreak, and a similar 
instance some years before. 

In Lagrange Co., Ind., 8 in 1902, there were three outbreaks 
in a school, apparently caused by the teacher, in whose nose 
diphtheria bacilli were found, and who had shown no symp- 
toms but a slight cold. In Boston 9 a boy who had recovered 
from diphtheria, escaped from isolation and went to Brock- 
ton, and within four days three clinical cases developed in the 
house where he visited. Fischer 10 reports an outbreak traced 
to a restaurant in which were several carriers and mild sore 
throats. Solberg 11 had a boy who caused several cases of the 
disease. He had been kept in the hospital for several months, 
but was finally discharged with the bacilli present. Cob- 
bett's 12 outbreak in Cambridge was due to a boy apparently 

1 Prelim. Rep. on Diphtheria in Well Persons, J. Mass. Ass. Bds. 
Health, Bost., 1901, XI, 9. 

2 Rep. Bd. Health, Lowell, 1904, 24. 

3 Prelim. Rep. on Diphtheria in Well Persons, J. Mass. Ass. Bds. 
Health, Bost., 1901, XI, 9. 

4 Pediatrics, N. Y., 1901, XII, 366. 

5 Rep. St. Bd. Health, Cal., 1906-08, 198. 

6 Armstrong, Austral. M. Gaz., Melbourne, 1908, XXVII, 350. 

7 Report of Epidemic of Diphtheria at Willard State Hospital by 
Russell and Salmon [Rep. State Com. on Lunacy, XVI], 35 of Reprint. 

8 Letter from Dr. H. N. Hurty, Sec. Ind. St. Bd. Health, 1907. 

9 Prelim. Rep. on Diphtheria in Well Persons, J., Mass. Ass. Bds. 
Health, Bost., 1901, XI, 9. 

10 Fischer, Miinchen med. Wchnschr., 1906, LIII, 250, 314. 

11 Solberg, quoted in Pub. Health, Lond., 1902-03, XV, 515. 

12 Cobbett, J. Hyg., Cambridge, 1901, I, 229. 



70 THE SOURCES AND MODES OF INFECTION 

well, but who for some weeks had had a slight nasal discharge 
in which diphtheria germs were present. Williams * notes a 
case in which a teacher was infected with clinical diphtheria 
by the nasal discharge of a pupil containing atypical bacilli. 2 
Newsholme 3 saw a case of diphtheria in February, 1901, 
which had ear discharge for a short time only. Suppuration 
recurred April, 1904, and diphtheria germs were present. 
Three cases of the disease occurred in the family soon after. 
The ear again discharged in March, 1906, with bacilli pres- 
ent, and a sister apparently contracted the disease from this 
source. Newsholme had a similar case in 1907. Vance 4 
states that a nurse had diphtheria in June, and after one 
negative culture from the throat, went home and infected 3 
persons. In August she returned to the hospital and infected 
4 other persons, at which time a culture from throat and nose 
was negative. Subsequent cultures proved positive, and 
continued so until late in November. Strain 5 also reports a 
nurse in whose nose diphtheria bacilli were found intermit- 
tently for nine months, but they were never present in the 
throat. Edsall 6 notes five outbreaks due to carriers, and 
Solis-Cohen 7 seven such outbreaks. Cameron 8 reports that 
in 70 instances cases of scarlet fever discharged from the Lon- 
don hospitals carried diphtheria to their homes, and that in 
many of these carriers diphtheria bacilli were shown to be 
present. 

Similar cases in which clinical diphtheria is apparently con- 
tracted from perfectly well convalescents or carriers, or from 
slight unnoticed sore throat, or from rhinitis, are found scat- 

1 Williams, J. Laryngol., Lond., 1905, XX, 591. 

2 Wesbrook's D^ 2 . 

3 Newsholme, Rep. Med. Off. Health, Brighton, 1906, 13. 

4 Vance, Intercolon. M. J. Australas., Melbourne, 1908, XIII, 152. 

5 Strain, Lancet, Lond., 1908, II, 1143. 

6 Edsall, J. Am. M. Ass., Chicago, 1909, LII, 125. 

7 Solis-Cohen, J. Am. M. Ass., Chicago, 1909, LII, 111. 

8 Cameron, Rep. to Asylums Bd. on Return Cases of Scarlet Fever 
in London, 1901-02, 41. 



CARRIERS AND MISSED CASES 71 

tered through medical literature, and a number of such have 
been collected by the Massachusetts Association of Boards 
of Health, 1 Nuttall and Graham-Smith, 2 Newsholme, 3 Sit- 
tler, 4 Niven, 5 Schneider, 6 myself 7 and others. 

Chronic Diphtheria. — Diphtheria sometimes assumes a 
chronic form, with few constitutional symptoms, and little 
that is noticeable, and nothing that is characteristic in the 
fauces. This condition may continue for months, and is 
sometimes accompanied by considerable antitoxin in the 
blood. Such cases may cause typical diphtheria. 8 

Glanders. — According to veterinary writers 9 the infec- 
tion of glanders often remains latent, and also many mild 
chronic cases occur which are the source of considerable out- 
breaks. The Bureau of Animal Industry 10 reports an instance 
where a horse was apparently infectious for eight years with- 
out manifesting any symptoms which would lead even an 
expert to suspect the infection. Another instance was given 
of a year-long infection of an apparently well animal. 

Influenza. — The rapidity with which epidemic influenza 
spreads, its sudden contemporaneous appearance at many 
distant points, and the difficulty of tracing the route of infec- 
tion, render it almost certain that there must in this disease 
be many mild atypical cases, and many persons infected, but 
showing no symptoms. That the disease is not carried by 

1 Prelim. Rep. on Diphtheria Bacilli in Well Persons, J. Mass. Ass. 
Bds. Health, Bost., 1901, XI, 9. 

2 Nuttall and Graham-Smith, The Bacteriology of Diphtheria, Cam- 
bridge, 1908, 311. 

3 Newsholme, Address at Victoria Univ., Manchester, Mar. 9, 1904, 
and Med.-Chir. Tr., Lond., 1904, LXXXVII, 549. 

4 Sittler, Miinchen med. Wchnschr, 1906, LIII, 863. 

5 Niven, Rep. on the Health of Manchester, 1908, 204. 

6 Schneider, Ztschr. f. Med.-Beamte, Berl., XX, 698. 

7 Rep. Supt. Health, Prov., 1897, 19; 1898, 23; 1905, 32. 

8 Neisser and Kahnert, Deutsche med. Wchnschr., 1900, XXVI, 
525, and Neisser, Deutsche med. Wchnschr., 1902, XXVIII, 719. 

9 Law, Text-Book of Veterinary Medicine, Ithaca, 1902, IV, 235. 

10 U. S. Dept. Agric, Bu. An. Ind., Circ. No. 78, 4. 



72 THE SOURCES AND MODES OF INFECTION 

the air over long distances, as has been urged by many, but 
is invariably transmitted by persons, has been shown by Par- 
sons, Schmid and others. That these persons often show no 
symptoms, and are not suspected of being carriers, also seems 
certain. 

There is some bacteriological evidence of this, but the bac- 
teriologists have not given to the study of this disease the 
attention which it deserves. Finkler found the bacillus in 
the sputum a year after the beginning of an attack. Lord, 1 
during non-epidemic periods, in examining cases of what 
appeared ordinary cough, found influenza bacilli present in 
60 per cent of the cases. Later, 2 in 186 non-tuberculous cases, 
mostly bronchitis, he found the bacillus frequently present, 
often in almost pure culture. Boggs 3 has also found chronic 
cases somewhat simulating tuberculosis, in one instance last- 
ing for a year. Holt, 4 in the Babies' Hospital in New York, 
obtained 112 positive cultures out of 312 taken from 198 
persons. Of 48 healthy persons 16 yielded positive cultures. 
I have found scarcely any other reports of the examination 
of well persons for this organism, but the frequency with 
which it is found in those sick with other diseases is evidence 
of the widespread distribution of the bacillus. Wollstein, 5 by 
swabbing the throat, found the bacillus in 16 of 37 cases 
of pneumonia, in 11 of 34 of bronchitis, in 8 of 18 cases of 
measles, in 8 of 16 of tuberculosis, but only 5 times in 65 cases 
of other diseases. Davis 6 found influenza-like bacilli in normal 
throats, and in 61 of 68 cases of whooping cough and in 13 
of 23 cases of measles. Inoculated on the mucous surface of 
a healthy young man, fever and catarrhal symptoms devel- 
oped. Both Davis and Wollstein consider that the so-called 

i Lord, Boston M. & S. J., 1902, CXLVII, 662. 

2 Lord, Boston M. & S. J., 1905, CLII, 574. 

3 Boggs, Am. J. M. Sc, Phila., 1905, n. s., CXXX, 902. 

4 Holt, Am. J. Obst., N. Y., 1909, LX, 343. 

6 Wollstein, J. Exper. M., N. Y., 1906, VIII, 681. 

6 Davis, J. Am. M. Ass., Chicago, 1907, LXVIII, 1563. 



CARRIERS AND MISSED CASES 73 

pseudo-iDfluenza bacilli in their different forms are of the 
same " species " as the typical forms. Others have found 
the bacillus in other infectious diseases, as Leibscher l and 
Auerbach, 2 the latter of whom obtained it in 5.4 per cent of 
700 cases of diphtheria, scarlet fever, etc. 

The Coccus of Pneumonia. — That the pneumococcus is 
present in the saliva of normal mouths was early recognized 
by Pasteur, Sternberg, Welch and others, and is, of course, a 
now well-established fact. Recently a number of careful 
observations have been made to determine the frequency of 
its occurrence, its virulence, and variations in form and habits 
of growth. Buerger 3 found it present in 50 per cent of 78 
normal mouths, and in 34.8 per cent of 204 normal throats 
not so carefully examined. He also found that it could be 
recovered for weeks from convalescents. Of the cultures from 
normal mouths 79 per cent proved virulent. Hiss 4 found it 
in 14 of 22 persons, and Duval and Lewis 5 in all of 24 per- 
sons about the laboratory. Lorrgcope and Fox 6 obtained it in 
40 per cent to 50 per cent of mouths examined. It was more 
often found and more virulent in winter. Frost, Divine and 
Reineking 7 found it in 36 per cent of healthy mouths, 23 per 
cent in autumn, 43 per cent in winter and 50 per cent in the 
spring. The organism may persist in the same individual 
for months. Park and Williams 8 report the pneumococcus 
as prevalent both in city and country, as do others, but note 
that germs from normal mouths are less virulent for rabbits 

1 Leibscher, Prag. med. Wchnschr., 1903, XXVIII, 85. 

2 Auerbach, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1904, 
XLVII, 259. 

3 Buerger, J. Exper. M., N. Y., 1905, VII, 497. 

4 Hiss, J. Exper. M., N. Y., 1905, VII, 547. 

6 Duval and Lewis, J. Exper. M., N. Y., 1905, VII, 473. 

6 Longcope and Fox, J. Exper. M., N. Y., 1905, VII, 430. 

7 Frost, Divine and Reineking, J. Infect. Dis., Chicago, 1905 [Suppl. 
No. 1], 298. 

8 Park and Williams, J. Exper, M., N. Y., 1905, VII, 403. 



74 THE SOURCES AND MODES OF INFECTION 

than those from cases of pneumonia. Wells l found pneu- 
mococcal in the throat or upper respiratory passages in 45 per 
cent of 135 persons, and Besser 2 found them in 14 per cent 
of the noses of 57 well persons, and Hasslauer 3 in 24 of 111 
normal noses. Ruediger 4 got positive results in 90 per cent 
of 51 normal throats, in 91.4 per cent of 71 scarlet fever 
throats, in 12 of 14 cases of measles, and in 8 of 9 cases of 
tonsillitis, or pharyngitis. 

Gonorrhea. — That gonorrhea assumes a latent form in 
both men and women, showing no signs whatever for con- 
siderable periods, and relapsing into a subacute or even acute 
condition after it was supposed to be cured, has long been 
known. But it is only since the discovery of the gonococcus 
that the latency of this infection, as well as its persistence, 
has been fully appreciated, just as it has only been the rec- 
ognition of this coccus which has shown the serious patho- 
logical changes in important organs which often follow 
gonorrhea. There has also been demonstrated recently the 
frequent innocent transmission of the disease among young 
children. All the text-books and monographs dealing with 
gonorrhea dwell on these facts, and refer to the finding of 
the germ in cases long supposed to be well, and to its per- 
sistence for long periods of time. 5 A physician told me of a 
case lasting from the third year of life to the twenty-eighth. 
Some striking instances of the latency of gonorrhea are given 
by Chapman, 6 and he has shown me records of many more 
in which unsuspected infection had lasted for many years. 
The same author states that the gonococcus may be encysted 

1 Wells, J. Am. M. Ass., Chicago, 1905, XLIV, 361. 

2 Besser, Beitr. z. path. Anat. u. z. allg. Path., Jena, 1889, VI, 331. 

3 Hasslauer, Centralbl. f. Bakteriol. [etc.], 1st Abt. Ref., Jena, 1905, 
XXXVII, 1. 

4 Ruediger, J. Am. M. Ass., Chicago, 1906, XLVII, 1171 

5 Wertheim, Arch. f. d. Geburtsh., Jena, 1902, XLII, 192. 

• Chapman, Fiske Fund Prize Essay, Providence, 1905, The Sequelae 
of Gonorrhea, etc., 31. 



CARRIERS AND MISSED CASES 75 

or dormant in tubal or ovarian tissue indefinitely. Rathbun 
and Dexter 1 from a clinical and careful bacteriological study 
of cases show that infection often persists long after the 
patient is apparently cured, and that such uncured cases are 
far more common than is generally believed. Hamilton 2 
refers to the difficulty of demonstrating the coccus in mild 
and chronic cases, and states that such cases are very com- 
mon. Nottshaft 3 followed 120 cases of gonorrhea and ob- 
tained the gonococcus from 73 per cent during the second 
six months. During the fourth six months the percentage 
fell to 18, and in the third year the gonococci still per- 
sisted in 6 per cent of the cases. This latency is the chief 
cause of innocent marital infections. It is also one reason 
why the medical supervision of prostitution can never 
have much effect in restricting the disease. No practicable 
amount of inspection would ever guarantee freedom from 
infection. 

Tubercle Bacilli in Mouth and Nose. — There are two 
conditions under which tubercle bacilli may exist in human 
beings without appreciable symptoms. 

First, they may be found on the mucous surfaces of mouth, 
throat, or nose. Straus 4 examined the nose of 29 well per- 
sons, orderlies, nurses and physicians about tuberculosis 
wards, and recovered tubercle bacilli from 9. Cornet found 
them in his own nose. Jones, 6 by inoculating animals with 
mucus from the nose of 31 persons not brought into par- 
ticularly close contact with consumptives, demonstrated the 
presence of tubercle bacilli in 11. Similar results have been 

1 Rathbun and Dexter, N. York M. J. [etc.], 1909, XC, 241. 

2 Hamilton, J. Infect. Dis., Chicago, 1908, V, 134. 

3 Nottshaft, Die Chronische Gonorrhea der Mansliche Harnrohre, 
Leipzig, 1905. 

4 Straus, Arch, de med. exper. et d'anat. path., Par., 1894, VI, 633. 

5 Cornet, Nothnagels Encyclopedia, Phila. and Lond., 1907, Tuber- 
culosis, 152. 

8 Jones, Med. Rec, N. Y., 1900, LVIII, 285. 



76 THE SOURCES AND MODES OF INFECTION 

reported by Moller 1 and Bernheim. 2 Persons in the vicinity 
of consumptives must, unless great care be taken, receive a 
certain number of tubercle bacilli upon their mucous sur- 
faces. Whether they increase in numbers in such a location 
is not shown by the observers quoted, but unless they do it 
seems rather surprising that they can be demonstrated in 
such a proportion of cases. On the other hand, it does not 
seem likely that conditions in the mouth and nose are favor- 
able for -the growth of this bacillus, and the weight of evi- 
dence seems to be that the tubercle bacillus does not, to any 
extent at least, develop on the normal mucous membrane 
of the throat or nose of well persons. 

Blair 3 reports finding tubercle bacilli in the nose of various 
wild animals in captivity. 

Latent Tuberculosis. — That the tubercle bacilli invade 
the tissues and, creating little disturbance, remain latent for 
a considerable period of time, has been amply demonstrated. 
While there are not many who believe that this latency is 
so universal or so persistent as does von Behring, yet it is 
certainly not a rare phenomenon. L. Rabinowitsch 4 in a 
recent article gives a short resume of the work of various 
observers, and Harbitz 5:: has also discussed it in an article 
on tuberculosis of children. Harbitz, in 142 autopsies of chil- 
dren who were clinically free from tuberculosis, and in whose 
glands no macroscopic or microscopic signs of the disease 
could be seen, nevertheless was able by inoculation to dem- 
onstrate the presence of virulent tubercle bacilli. Rabino- 
witsch reports four cases of virulent bacilli in lymph glands 
that had undergone calcareous degeneration, thus indicating 
a long-standing latency. Many similar observations by other 

1 Moller, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXXII, 
205. 

2 Bernheim, Clinique, Brux., 1905, XIX, 346. 

3 Blair, J. Comp. M. & Vet. Arch., 1903, XXIV, 278. 

4 Rabinowitsch, Berl. klin. Wchnschr., 1907, XLIV, 35. 

5 Harbitz, J. Infect. Dis., Chicago, 1905, II, 143. 



CARRIERS AND MISSED CASES 77 

writers are given by those just quoted, and Gaffky 1 has 
recently reported finding the glands of 11 per cent of 246 well 
persons as containing living bacilli, demonstrated by inocu- 
lation tests. . Tubercle bacilli are found in the tonsils as well 
as in the lymph glands. Lartigau and Nicoll 2 found infected 
adenoids in 12 of 75 healthy children, and Weichselbaum and 
Bartel, 3 Goodale 4 and Cornet 5 report similar findings. 

Leprosy. — Sticker 6 says that lepra bacilli often remain 
latent in the nose for long periods. 

Bacteria of Suppuration, Latency. — As has been stated on 
page 20, pus bacteria are normal inhabitants of the skin and 
mucous surfaces, and may even invade the glands and other 
deeper tissues and remain latent for long periods of time. 
They may later, as the result of traumatism, be carried by 
the circulation to distant organs, there causing suppuration. 7 
Among those who have demonstrated the latency of infection 
with pus-forming bacteria may be mentioned Manfredi and 
Viola, 8 Kalble, 9 Perez 10 and Hess. 11 Conradi 12 seems to have 
employed an improved technique in his work, and has demon- 
strated bacteria in 72 of 162 apparently healthy organs taken 

1 Gaffky, Konferenz Internat. f. Tuberk., Wien, 1907. 

2 Lartigau and Nicoll, Am. J. M. Sc, Phila., 1902, n. s., CXXIII, 
1031. 

3 Weichselbaum and Bartel, Wien klin. Wchnschr., 1905, XVIII, 241. 

4 Goodale, Boston M. & S. J., 1906, CLV, 278. 

6 Cornet, Nothnagels Encyclopedia, Phila. and Lond., 1907, Tuber- 
culosis, 158. 

6 Sticker, Arb. a. d. k. Gesndhtsamte., Berl., 1899, XVI, Anlage I. 

7 Soprano, Centralbl. f. Bakteriol. [etc.], 1st Abt. Orig., Jena, 1906, 
XLI, 601. 

8 Manfredi and Viola, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 
1899, XXX, 64. 

9 Kalble, Miinchen med. Wchnschr., 1899, XLVI, 622. 

10 Perez, Jahresb. u. d. Fortschr. . . . d. path. Mik. Baumgarten, 
1897, XIII, 894. 

11 Hess, Centralbl. f. Bakteriol. [etc.], 1st Abt. Orig., Jena, 1907, 
XLIV, 1. 

12 Conradi, Miinchen med. Wchnschr., 1908, LV, 1523. 



78 THE SOURCES AND MODES OF INFECTION 

from 150 healthy animals. Ford 1 and Dudgeon 2 also report 
finding bacteria, especially pus-forming types, lying latent in 
healthy organs. Bardley 3 found bacteria pathogenic for rab- 
bits in 196 of 200 atrophied tonsils, and in 101 he demon- 
strated Streptococcus pyogenes. 

Latent Tetanus. — Canfora 4 and Vincent 5 have both 
shown that tetanus spores may be injected into the body 
and remain latent for some time. 

Latency a Common Phenomenon. — The carrying of pus- 
forming organisms and tubercle bacilli without symptoms, 
and the latency of both infections, are of little practical im- 
portance to the health officer, for such latent infections are 
not a source of danger to others. The fact of the latency is 
touched upon here to show how general is the phenomenon. 
The laity and a large number of physicians are incredulous 
that there should be diphtheria infection unless the patient 
is sick in bed with the throat choked with exudation, or that 
there can be scarlet fever without high fever and extensive 
eruption. It is to show to such that latency, and infection 
with slight symptoms, are phenomena belonging not only to 
diphtheria, typhoid fever and scarlet fever, but to many other 
infectious diseases, that these facts are here presented. 
Infection without symptoms is no cause for surprise, but 
may be expected in any parasitic disease. There may be 
exceptions, as is said to be the case in relapsing fever, 
but these exceptions, rather than the existence of latency 
and atypical types, should be cause for surprise. 

Likeness of Scarlet Fever and Diphtheria. — Unfortunately 
we do not know the nature of scarlet fever virus, hence many 
important matters relating to the causation of this disease 

1 Ford, J. Hyg., Cambridge, 1901, I, 277. 

2 Dudgeon, Lancet, Lond., 1908, II, 1651. 

3 Bardley, Johns Hopkins Hosp. Bull., Bait., 1909, XX, 88. 

4 Canfora, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1907, 
XLX, 495. 

5 Vincent, J. de physiol. et de path, gen., Par., 1908, X, 664. 



CARRIERS AND MISSED CASES 79 

are in doubt. There are many points of resemblance between 
this disease and diphtheria, such as the degree of infective- 
ness, the apparent variation in the period of incubation and 
duration of infection, the very brief incubation in some cases, 
the persistence of infection in some instances long after recov- 
ery and the contrary fact of the early loss of infectivity in 
many instances, the prominence of the initial throat symp- 
toms, and the occurrence of albuminuria and middle ear 
inflammations. We are justified, I think, in looking for a bac- 
terial infection, and the probability is that scarlet fever is 
in the main, like diphtheria, a local disease of the mucous 
surfaces, chiefly of the throat and nose. We certainly see 
many mild atypical cases of scarlet fever just as we do of 
diphtheria, probably fully as many, and we naturally expect 
to find also true carriers who exhibit no symptoms at all. 

Atypical Scarlet Fever. — As the bacteriologist cannot help 
us, we have to rely on clinical evidence, which is much more 
uncertain and difficult to secure. The layman and the inex- 
perienced physician are apt to scoff at the suggestion of scarlet 
fever unless the patient has a high fever and is as red as a 
lobster. But all who have seen much of this disease know 
that it is exceedingly common to see cases with a scarcely 
discernible indefinite rash lasting for only a few hours, a rise 
in temperature of only a degree or two lasting also only a 
few hours, and the merest trace of sore throat. Sometimes 
the rash may be entirely absent and even the fever may 
escape the most careful observation. 1 In institutions and 
families, such cases, considered doubtful at first, or perhaps 
entirely neglected, prove to be the origin of typical symptoms 
in others. Every health officer will recall many such cases. 
They are the missed cases which are such a factor in the 
maintenance of this disease. There are many references to 
them in the reports of health officers and in medical litera- 
ture. Among others who report such atypical cases are News- 

1 Caziot,Bull. et mom., Soc. med.d. hop. de Par., 1903, n.s., XX, 799; 
Semaine med., Par., 1903, XXIII, 205. 



80 THE SOURCES AND MODES OF INFECTION 

holme, 1 Caziot, 2 Welch and Schamberg, 3 Cameron, 4 Butler 5 
and Thornton and Mader referred to below. In most of 
these missed cases there were some slight symptoms, though 
overlooked or misunderstood at the time. In Manchester, 
in 1906, there were discovered 229 missed cases, mostly of a 
mild character. From these 139 other cases had developed. 6 
Number of Atypical Cases. — It is difficult to estimate the 
number of atypical cases of scarlet fever. Probably it 
varies according to the extent and severity of the outbreak, 
and for other reasons. Newsholme 7 has reported a milk out- 
break in which the number of sore throats without the pres- 
ence of eruption was 215, while the number of typical cases of 
scarlet fever was only 38. Butler, 8 at Wellesden, studied the 
incidence of sore throat in families where there was reported 
scarlet fever, and found that 31.2 per cent of 1266 persons in 
such families had sore throat, while only 2.8 per cent of 1644 
persons living in families where there was no scarlet fever 
had sore throat. In a school with 300 children Thornton 9 
found 31 typical cases, 19 cases with no rash and slight sore 
throat, and 46 cases in which only desquamation was noticed. 
Mader 10 observed 9 typical and 12 very atypical cases in an 
outbreak in a home for epileptics. True " carriers," that is, 
perfectly well persons, are sometimes reported. Thus I have 
noted an instance where a woman apparently in this way 
carried scarlet fever to her child. She had been taking care of 

1 Newsholme, Tr. Med.-Chir. Soc, Glasg., LXXXVII, 549. 

2 Caziot, Bull, et mem., Soc. med. d. hop. de Par., 1903, n.s., XX, 799; 
Semaine med., Par., 1903, III, 205. 

3 Welch and Schamberg, Acute Infectious Diseases, Phila., 1905, 390. 

4 Cameron, Rep. on Return Cases of Scarlet Fever and Diphtheria 
to Asylums Bd., Lond., 1901-02, 38, 78. 

6 Butler, Proc. Roy. Soc. Med., Lond., 1908, I, Epidemiol. Sec, 225. 

6 Rep. on Health of Manchester, 1906, 43. 

7 Newsholme, Rep. Med. Off. Health, Brighton, 1906, 48. 

8 Butler, Rep. Med. Off. Health, Wellesden, 1907, 76. 

9 Thornton, Brit. M. J., Lond., 1908, I, 495. 

10 Mader, Cor.-Bl. f. schweiz. Aerzte, 1908, XXXVIII, 169. 



CARRIERS AND MISSED CASES 81 

another child, and after an entire change of clothing, bath and 
shampoo, visited the first-named child, who was taken sick two 
days later. Newsholme reports what he thinks are possibly, 
or even probably, similar cases. Newman, 1 of Finsbury (Lon- 
don), noted 5 carriers among school children, three of whom, 
though they had never had the disease, transmitted it to 
others. Kerr 2 also reports 5 such cases. When a diphtheria 
patient discharged from a hospital carries scarlet fever home 
to his family, he must in most instances be considered a true 
carrier, for it is unlikely that symptoms of scarlet fever would 
often escape notice in the hospital. Ten of this sort of return 
carriers are reported by Simpson, 3 30 by Cameron 4 and 44 
by Turner. 

Smallpox. — There is still doubt as to the specific cause 
of smallpox. The claims that have been advanced in favor 
of this or that micro-organism have not as yet been substan- 
tiated. Hence there is no " laboratory " evidence that car- 
riers of this disease exist, nor is there much clinical evidence 
that perfectly well persons transmit the disease. There are, 
it is true, scattered through medical literature numerous 
reports of instances of such transmission. These reports, as 
often in other diseases, are, as regards the evidence, rather 
unsatisfactory. There is usually a possibility of such trans- 
mission, no actual demonstration. Nevertheless it is quite 
possible that there may be true carriers of smallpox, and 
there may be a considerable number of them. Mild cases 
are often very numerous. This was well illustrated in the 
recent epidemic in the United States and England. In the 

1 Newman, Rep. Med. Off. Health, Lond., 1904, 27. 

2 Kerr, Rep. Med. Off. Education, Lond., 1907, 43. 

3 Simpson, Rep. on Return Cases of Scarlet Fever and Diphtheria 
to Asylums Bd., Lond., 1898-99, 8. 

4 Cameron, Report on Return Cases of Scarlet Fever and Diphtheria 
to Asylums Bd., Lond., 1901-02, 43. 

6 Turner, Rep. on Return Cases of Scarlet Fever and Diphtheria to 
Asylums Bd., Lond., 1902-04, 3. 



82 THE SOURCES AND MODES OF INFECTION 

United States in the year ending June 30, 1901, the fatality 
in 38,506 cases was only 1.79 per cent. At such a time great 
numbers of cases escape recognition. The patients often 
have no idea that they are sick with a dangerous disease. 
They may be at their work even during the prodromal stage. 
There may be only half a dozen, or even fewer, atypical 
pustules. I have in rather a limited experience seen several 
such cases. They are also reported by Welch and Scham- 
berg. 1 These authors also state that cases occur where there 
is no eruption at all. The step from half a dozen points of 
eruption to none at all is so slight, and the extremely mild 
cases at times are so numerous, that a considerable num- 
ber sine eruptione may reasonably be expected. Armstrong 2 
recently reports three such cases with some fever and sub- 
jective symptoms but no eruption. They occurred in infected 
families and subsequently proved refractory to vaccination. 

Measles. — There is little clinical evidence that ''carriers" 
of measles are common. Most health officers consider that 
measles is rarely carried by a " third person." It usually 
has a quite definite clinical picture. In Aberdeen, so Dr. 
Matthew Hay writes to me, judging from a census taken in 
certain schools, it was estimated that from 90 to 93 per cent 
of the children over ten years of age had had a recognized 
attack of measles. That such a high percentage of children 
had recognized attacks, indicates that atypical cases cannot 
be very common. Mild, atypical and unrecognized cases of 
this disease must be far less numerous than are such cases 
in scarlet fever, diphtheria and typhoid fever. 

Protozoan Diseases. — Although the marks of distinction 
between animal and vegetable life as seen among the lower 
forms are ill defined and uncertain, yet it is generally agreed 
that though the group of organisms known as bacteria have 
characters belonging to both the vegetable and the animal 
kingdom, they are more nearly allied to the former, while an- 

1 Welch and Schamberg, Acute Infectious Diseases, Phila., 1905, 207. 

2 Armstrong, Arch. f. Diagnosis, 1909, II, 126. 



CARRIERS AXD MISSED CASES 83 

other group, known as protozoa, are allied to the lower forms 
of animal life. Although one of the latter class was discovered 
to be the cause of malaria in 1880, at a time when most of the 
disease-producing bacteria were unknown, the bacteria have 
received far more study, and indeed it is only recently that 
the protozoa as the cause of disease have received much atten- 
tion. It is known that a number of diseases both of men and 
of animals are caused by protozoa of various types. As has 
recently been emphasized by Daniels, 1 latency is a common 
phenomenon of protozoan infection, and is of the utmost im- 
portance from an epidemiological standpoint. Not only do 
the blood parasites maintain long continued infection with 
few symptoms, but such forms as Ameba, Balantidium, and 
Lamblia live in the intestines indefinitely, reproducing them- 
selves asexually. A number of the diseases to be referred to 
do not affect man, but they serve to illustrate the prevalence 
of latency in protozoan infections. 

Texas Cattle Fever. — It has long been recognized that 
the Texas fever of cattle could be transmitted by apparently 
healthy animals. The explanation of this fact was not, how- 
ever, forthcoming until Smith and Kilborne's 2 classical re- 
searches in 1893 demonstrated that the disease was due to 
a blood parasite, a protozoan (Piroplasma bigeminum) , not a 
bacterium, and also demonstrated that it is only transmitted 
from animal to animal by means of a species of tick (Boophi- 
lus annulatus), in which the parasite passes through a cycle 
of changes necessary for the maintenance of the species. This 
work of Smith and Kilborne's was one of the most important 
steps in the development of our knowledge of the insect 
carriage of disease, a knowledge which has been of such inesti- 
mable value in connection with malaria, sleeping sickness, yel- 
low fever and other blood diseases. It was soon determined 
that animals which had recovered from Texas fever and were 

1 Daniels, Brit. M. J., Lond., 1909, II, 767. 

1 Smith and Kilborne, U. S. Dept. Agric, Bu. An. Ind., Bull. No. 1, 
1893, 57. 



84 THE SOURCES AND MODES OF INFECTION 

immune to it, carried the piroplasma in the blood for an 
indefinite time. In one instance it was known to have re- 
mained for thirteen years. 1 Reports from the Philippines 2 
show that many of the cattle in those islands are infected 
with the parasites of Texas fever though showing no symp- 
toms. 

East Coast Cattle Fever. — A disease much like our Texas 
fever is known as East Coast African cattle fever. It is due 
to a slightly different form of piroplasma and is transmitted 
by a native tick. The principal source of infection is the 
native animals which are immune and whose blood contains 
the organisms of the disease. 3 

Malaria. — The most important of the protozoan diseases 
is malaria. It had always been believed that this disease 
might remain latent for months and years, but what latency 
really meant could not be determined until after the dis- 
covery of the specific cause of the disease. Many of the 
protozoa pass through various metamorphoses, or fixed cycles 
of development, and it was found that in malaria the Plas- 
modium, which is its cause, may in certain stages persist in 
the blood or organs of the body without causing any charac- 
teristic symptoms, or indeed any symptoms at all. Then at 
any time, from one cause or another, its reproduction may 
again become active and more or less marked symptoms 
appear. Thus relapses may occur after a period of several 
years, when the bodily resistance is from any cause impaired. 
Thus fever after surgical operation is not rarely due to a 
latent malaria becoming active, the parasite being found in 
the blood and the symptoms yielding to quinia. As malaria 
is a strictly transmissible disease, the Plasmodium which 
causes it being borne from one person to another by mosqui- 
toes, a latent case of the kind described may be, and doubt- 
less often is, the means of introducing the disease into hitherto 

1 U. S. Dept. Agric, Rep. Bu. An. Ind., 1904, XXI, 26. 

2 Bull. 14, Bu. Gov. Lab., Manila, P. I., 1904, 11. 

3 Bruce, Nature, Lond., 1905, LXXII, 496. 



CARRIERS AND MISSED CASES 85 

uninfected localities. Unless such cases drift into hospitals, 
they are almost certain to be unrecognized. Craig 1 made a 
careful study of 424 such latent cases found among 1653 sol- 
diers examined in the Philippines. Since I first wrote this 
chapter Craig's book has appeared in which he discusses in 
much detail latency and recurrences. 2 He has noted an asex- 
ual conjugation of the parasites in the blood cells, which is 
followed by a resting stage, and which he believes has some 
relation to the latency of the infection. Where malaria pre- 
vails extensively, as in the tropics, it has long been noticed 
that a large part of the adult population is immune. It is 
now known that this immunity is to a large extent acquired, 
and is due to the invasion of the body in infancy by the 
parasites. This invasion, while sometimes causing symptoms 
and death, frequently gives rise to few or no symptoms, or 
if some reaction appears at first, it soon disappears, and the 
children may seem perfectly well though the parasites are 
constantly found in the blood. They disappear year by year 
and infection is rarely found after adolescence. Koch 3 in 
Africa found large numbers of children infected, even as high 
as 100 per cent. Plehn 4 found many adults infected though 
not sick. Christophers and Stephens found the parasites in 
the blood of 90 per cent of infants examined in one locality 
on the Gold Coast in Africa, and the Thompson Yates ex- 
pedition to Nigeria reports finding them in 63 per cent of 
children under 3 years of age. Ziemann 7 found that in the 
Cameroon county 37 per cent of children under 5 years of 

1 Craig, J. Infect. Dis., Chicago, 1907, IV, 108. 

2 The Malarial Fevers, N. Y., 1909, 228. 

3 Koch, cited in Thompson Yates' Lab. Rep., 1900, No. 4. 

4 Plehn, cited by Marchiafava and Bignani, Twentieth Cent. Prac- 
tice, XXI, 807. 

5 Christophers and Stephens, Reports of the Malarial Commission of 
the Roy. Soc. (Eng.), 2nd Ser., 1900-03, 15. 

6 Thompson Yates' Lab. Rep., 1900, III, Pt. 2, 201. 

7 Deutsche med. Wchnschr., 1900, XXVI, 399, 642, 753, 769. 



86 THE SOURCES AND MODES OF INFECTION 

age were infected. In Panama Kendall 1 found 57 per cent 
infected of the natives of all ages examined in the village 
of Bahio, and 73 per cent of foreigners. While many of 
the latter were more or less sick, many were entirely well. 
Darling 2 in villages in the Panama Canal zone where there 
were no Anopheles, nevertheless found that 10 per cent of 
the laborers at work were infected though they were not at 
all sick. Among the families of the Spanish and the West 
Indians, the latent infection reached 30 per cent. It is this 
latent infection in the blood of the native population which 
is the cause of the malaria which so certainly attacks arrivals 
from non-malarial regions. The greater the distance that can 
be placed between the natives and the strangers the less 
the danger of the latter contracting the disease. 

Sleeping Sickness. — African sleeping sickness has been 
shown to be due to a protozoan, Trypanosoma gambiense. 
This disease has been much studied of late, and it seems cer- 
tain that it is transmitted by means of the tsetse fly (Glossina 
palpalis) , though whether it is a purely accidental mechanical 
transference on the proboscis of the fly, or whether it passes 
through a part of its life history in the body of the fly, as 
the Plasmodium of malaria does in the mosquito, is still uncer- 
tain. In any event the parasite is frequently found in the 
blood of apparently healthy subjects, just as is the malarial 
parasite. According to Todd 3 it may remain in the blood 
for 15 years, causing no symptoms, and frequently remains 
for many months. The expedition from the Liverpool School 
of Tropical Medicine 4 found many natives infected, but who 
exhibited no symptoms, or only slight symptoms. The greater 
the prevalence of the disease the more common are these 
latent cases. In Gambia, where the disease is rare, not more 

1 Kendall, J. Am. M. Ass., Chicago, 1906, XLVI, 1151, 1266. 

2 Darling, J. Am. M. Ass., Chicago, 1909, LIII, 2051. 

3 Todd, Tr. Epidemiol. Soc, Lond., 1905-06, XXV, 1. 

4 Liverpool School Trop. Med. Memoirs, 1904, XIII; Med. News, 
N. Y., 1904, LXXXV, 526, 615. 



CARRIERS AND MISSED CASES 87 

than one native in 1000 examined showed the parasites, while 
in the Congo 46 in 100 were infected, and in Uganda the 
percentage was still higher. Whether the disease is always 
transferred from man to man, or whether some of the lower 
animals also harbor the parasites and thus serve as a " reser- 
voir " from which the human disease is derived, is as yet 
uncertain. 

Nagana. — Nagana 1 is an African cattle disease which, 
like the sleeping sickness, is caused by a trypanosome T. 
brucei, and is also transmitted by a tsetse fly, G. morsitans, 
though of another species. Wild herbivora are very generally 
infected with the specific trypanosome of this disease, but 
because of immunity, probably acquired, they show few or 
no symptoms. These carriers are the real source of the 
disease which so speedily attacks imported animals. 

Syphilis. — The spirochete of syphilis has in one instance 
been reported as remaining latent in a healed lesion of that 
disease. 2 

Amebic Dysentery. — There are two forms of dysentery, 
one caused by a bacillus and the other due to an ameba. 
The amebic form has been carefully studied by Musgrave 
and Clegg 3 in the Philippines. These authors are inclined 
to think that many of the amebse which are widely dissemi- 
nated in the Philippines are pathogenic for man. They may, 
however, often remain in the intestines for months without 
causing symptoms. They found amebae in 101 of 300 pris- 
oners. Of these 61 had had dysentery, 40 gave no history 
of dysentery, but of these 8 died of intercurrent affections, 
and dysenteric lesions were found in all. Of 32 others, 30 
later developed dysentery, and 2 passed from observation. 
These authors quote Celli and Fiocca, Strong and Musgrave, 

1 Minchin, Gray and Tullock, Proc. Roy. Soc, Lond., 1906; Nature, 
Lond., 1906, LXXVII, 57. 

2 Pasini, quoted by Rosenberger, N. York M. J. [etc.], 1908, 
LXXXVII, 394. 

3 Musgrave and Clegg, J. Infect. Dis., Chicago, 1905, II, 334. 



88 THE SOURCES AND MODES OF INFECTION 

Cunningham, and Grassi as also finding amebae in healthy 
persons. 

Percentage of Carriers of Amebae. — Walker l found 70 
per cent of 50 native soldiers in the Philippines infected with 
amebae, and 50 per cent of 50 American soldiers, though they 
were not sick with dysentery. Garrison 2 reports that 23 per 
cent of 4106 prisoners in the Philippines had amebse in their 
stools. Hoyt 3 examined the feces of 280 hospital patients, 
medical, surgical and venereal, and found amebae in 84, or 
30 per cent. Craig, 4 however, does not agree with Musgrave 
and Clegg, and Walker, but believes with Schaudinn that 
the ameba, Entameba coli, so frequently found in healthy per- 
sons, is a different species from E. histolytica, which is found 
only in cases of dysentery or in convalescents. This is also 
the view of Vedder. 5 Even if the contention of these latter 
authors is correct, and most of the intestinal amebae that 
are so commonly found in the tropics are distinct from the 
true dysentery ameba, it is certain that the latter is some- 
times found in persons for a long time after recovery, and 
may also be found in the feces before the disease develops. 
Martini 6 reports a case in which the sickness lasted from the 
15th of September to the 1st of December, 1907, but in which 
the amebae persisted until the last of January, 1908. Vin- 
cent 7 reports several instances in which persons were carriers 
for five months after their return to France from Tonkin. 
Lemoine 8 had under observation a man who contracted the 
disease in China in 1897 and returned to France and trans- 

1 Walker, J. Med. Research, Bost., 1907-08, XVII, 379. 

2 Garrison, Philippine J. Sc., Manila, 1908, III, 200. 

3 Hoyt, Philippine J. Sc, Manila, 1908, III, 417. 

4 Craig, J. Infect. Dis., Chicago, 1908, V, 324. 

6 Vedder, J. Am. M. Ass., Chicago, 1906, XLVI, 870. 

6 Martini, Arch. f. Schiffs- u. Tropen-Hyg., Cassel, 1908, XII, 588. 

7 Vincent, Bull. Soc. path, exot., Par., 1909, II, 78. 

8 Lemoine, Bull, et mem. Soc. med. d. hop. de Par., 1908, 3d Ser., 
XXV, 640. 



CARRIERS AND MISSED CASES 89 

mitted the disease to another in 1908. It seems probable 
that the cases which are occasionally noted in the northern 
United States are due to contact in some way with chronic 
carriers returned from the tropics. 

Yellow Fever. — The parasite which is the cause of yellow 
fever is still unknown, although fortunately for preventive 
medicine we have very accurate knowledge of the manner 
in which the disease is transmitted. As in scarlet fever, so in 
yellow fever, lack of knowledge of the parasite renders diffi- 
cult the recognition of carrier cases if they exist. But there 
is abundant clinical evidence that many very mild and atyp- 
ical cases occur which it is impossible to recognize. It is in 
young children chiefly that this slight disturbance is produced 
by the infection. A similar phenomenon is noted in malarial 
disease, and young children are the chief source of infection 
in both yellow fever and malaria. The fact of the mildness 
of these cases, their frequency, and the impossibility of mak- 
ing a diagnosis, has been insisted upon by Finlay, Gorgas, 
Guiteras, Carter, Agramonte, Marchoux and others. Brady 1 
states that the fatality among children is sometimes as low 
as 0.5 per cent. Even in adults, walking cases, which it is 
impossible to discover by an ordinary examination, are not 
rare. Thus it was claimed that during an outbreak in Louisi- 
ana a single walking case carried the disease to three different 
communities. Quarantine officers now take the temperature 
of each passenger, and in this way yellow fever cases are 
occasionally detected which would otherwise have walked 
ashore without exciting suspicion. 2 

Conclusions. — We are justified from the evidence pre- 
sented in coming to the following conclusions: 

1. Mild atypical and unrecognized cases of the infectious 
diseases are often extremely common. In many diseases they 
may be more numerous than the recognized cases. 

2. Disease-producing micro-organisms, whether bacteria 

1 Brady, N. Orl. M. & S. J., 1905-06, LVIII, 550. 

3 Doty, Am. Pub. Health Ass. Rep., 1905, XXXI, Pt. I, 261. 



90 THE SOURCES AND MODES OF INFECTION 

or protozoa, frequently persist in the body without causing 
symptoms. 

3. Sometimes the germs remain only a few weeks or months 
after convalescence, and sometimes they may persist for 
years, perhaps for life. Sometimes these carriers give no 
history of ever having been sick. 

4. While the bacteria found in carriers are sometimes lack- 
ing in virulence, many times they show the highest degree 
of virulence. 

5. There is ample epidemiological evidence that healthy 
carriers as well as mild unrecognized cases are the source of 
well-marked outbreaks. 

6. The number of carriers varies greatly in different dis- 
eases. From 20 to 50 per cent of the population are carriers 
of pneumococci. It seems probable that the influenza bacillus 
is as widely distributed. During outbreaks of cerebro-spinal 
meningitis the number of carriers may be from 10 to 30 times 
as numerous as the number of cases. Even when diphtheria 
is not prevalent 1 per cent of the population may be carrying 
the bacilli, and during outbreaks the number may be several 
times greater. Probably 25 per cent of all typhoid fever cases 
excrete bacilli for some weeks after convalescence, and it is 
estimated that from 1 in 500 to 1 in 250 of the population 
are chronic carriers. What little evidence there is indicates 
that carriers are as numerous in dysentery and cholera as 
they are in typhoid fever. In yellow fever, sleeping sickness, 
and particularly in malaria, carriers are very numerous. 
There is no evidence that there are many carriers of measles 
or smallpox. 

7. Any scheme of prevention which fails to take into ac- 
count carriers and missed cases is doomed to partial and 
perhaps complete failure. 



CHAPTER III. 

LIMITATIONS TO THE VALUE OF ISOLATION. 

Number of Mild Cases and Carriers. — In the first chapter 
the attempt was made to show that pathogenic organisms do 
not usually develop outside of the body. Except for a few 
diseases, or under unusual circumstances, the saprophytic 
existence of disease germs is not to be looked for. Such 
sources of infection are much rarer than is generally assumed, 
and for most diseases may be entirely neglected. In the 
second chapter, evidence was presented that certain other 
sources of infection are very much more numerous than is 
generally believed, and it is here contended that no scheme 
of sanitation can have a scientific basis, or can have any 
possibility of success, which does not take full cognizance of 
them. 

It must be admitted by all that mild atypical cases of con- 
tagious diseases are very numerous. Every one who has had 
any experience with the last epidemic of smallpox in the 
United States and England must have had many unpleasant 
reminders of this. Health officers' reports are full of instances 
of the introduction of the disease into a community by per- 
sons unsuspected by any one of having the disease, and who 
often give rise to a whole series of cases. Similar experiences 
with scarlet fever are often reported. The most critical inves- 
tigation, such as that of our surgeons in the Spanish War, 
indicates that mild unrecognized cases of typhoid fever fully 
equal, if they do not exceed, the number of cases which 
are recognized and reported. Even with every facility for 
diagnosis, the amount of sore throat due to the diphtheria 
bacillus, but not so* suspected, is fully equal to the amount 
of recognized diphtheria; and in many other infectious 

91 



92 THE SOURCES AND MODES OF INFECTION 

diseases these mild cases occur with varying degrees of 
frequency. 

Usually not Recognized. — The extent to which these mild 
atypical cases escape recognition varies with the disease, the 
social condition of the people affected, the intelligence and 
conscientiousness of the physician, and the attitude of the 
health officer. That the majority of people will not consult 
a physician unless they are decidedly sick, is certain. That 
they will refrain from doing so if they expect to be reported 
to the health officer and to be placed under various restric- 
tions, is but in accord with human nature. A slight sore 
throat, or a fleeting rash, little suggestive of danger, will be 
lightly passed over, no physician will be called and no pre- 
cautions taken, and often there will be no thought of danger 
to others. It has always been known that a certain number 
of mild cases, difficult to recognize, could be expected in 
almost all infectious diseases, but it remained for the labora- 
tory worker to show how numerous they are in such diseases 
as typhoid fever, diphtheria, plague and malaria. The micro- 
scopic demonstration of the frequency with which clinically 
unrecognizable attacks of the above named and other 
diseases occur, had called the attention of clinicians and epi- 
demiologists to their probable occurrence in such other dis- 
eases as scarlet fever, smallpox, and yellow fever, the specific 
organisms of which have not as yet been discovered. So that 
at the present time the most careful epidemiologists, clinicians 
and laboratory workers begin to realize that very large num- 
bers of mild atypical and unrecognizable cases are bound to 
occur in most infectious diseases. But as yet few text-books 
on sanitation, clinical medicine, or even on bacteriology, lay 
sufficient emphasis on this fact. Nothing is more common 
than to find the young man just from the medical school, as 
well as the old practitioner, quick to deny the presence of 
scarlet fever, diphtheria, or typhoid fever because the symp- 
toms are not severe enough or because they deviate too 
much from the text-book description. But the large number 



LIMITATIONS TO THE VALUE OF ISOLATION 93 

of the mild and aberrant cases, which usually remain " missed 
cases," and their importance in the extension of the infectious 
diseases, must now be admitted. 

Carriers Exceedingly Numerous. — Still more numerous 
are the pure carriers, those persons in whose bodies the 
pathogenic bacteria and protozoa develop without causing 
symptoms. The recognition of this element of danger is due 
entirely to laboratory investigation, but, strange to say, most 
workers on bacteriology lay no more stress on this epidemio- 
logical factor than do the writers of treatises on hygiene or 
of text-books of medicine. In the preceding chapter sufficient 
evidence was presented to demonstrate the very great fre- 
quency with which these carrier cases occur. Their exist- 
ence and the virulence of the germs which they carry are 
now established facts. Numerous instances were given where 
such carriers appeared to have transmitted the disease to 
others. Indeed it is almost inconceivable that it should be 
otherwise. It is hardly possible that virulent typhoid bacilli 
or diphtheria bacilli produced in large numbers, as they fre- 
quently are in carriers, should not be equally as dangerous as 
those which develop in the bodies of the sick. That is, they 
are equally dangerous potentially; actually the well person 
moving freely about may be more dangerous to the com- 
munity than the sick person who is confined to the house. 

Approaching the subject from another standpoint, it is 
interesting to see how the discovery of these missed and car- 
rier cases has explained so much which we formerly did not 
understand. 

Effort to " Stamp Out " Disease. — Twenty-five or thirty 
years ago we heard a great deal about " stamping out" the 
contagious diseases. That was the era of the building of hos- 
pitals for these diseases, of the organization of the sanitary 
service, of the discovery of pathogenic bacteria. The wonder- 
ful decrease in smallpox, the successful fight against cholera, 
the almost total disappearance of typhus fever, and the com- 
plete disappearance of plague, only foreshadowed, it was said, 



94 THE SOURCES AND MODES OF INFECTION 

the extermination of typhoid fever, diphtheria, scarlet fever 
and measles. It was claimed that in those diseases which 
are exclusively contagious, if every case can be isolated until 
it is free from infection, the disease will be exterminated. It 
was believed that if people, and especially physicians, would 
take only a little more care, practically all cases of these 
diseases could be recognized and isolated. It was also thought 
to be not very difficult to control them until infection had 
disappeared. This confidence in the efficacy of isolation was 
in the then existing state of knowledge not unreasonable. 

Isolation and its Results in Providence. — Previous to 
1884 there had been in Providence no isolation to speak of 
in any of the contagious diseases except smallpox. In fact 
very many physicians did not consider that scarlet fever and 
diphtheria were very contagious, if contagious at all, but 
were inclined to look upon them as filth diseases. Restric- 
tive measures, including isolation at home and fumigation, 
began to be applied in 1884 and were quite steadily strength- 
ened during the next sixteen or seventeen years. I hoped, 
as did most health officers, that if scarlet fever and diph- 
theria could not be stamped out, they could be reduced to 
an insignificant remnant. But they were not stamped out 
in Providence, as they have not been in other cities. On the 
contrary, we had twice as many deaths in 1887 from scarlet 
fever as we had had during any year for seven years. Diph- 
theria from 1886 to 1890 also caused nearly double the num- 
ber of deaths that it had in the preceding four years. Of 
course we talked about epidemic waves, and noted that the 
mortality from the last wave was very much lower than from 
many that had preceded it, and congratulated ourselves that 
the outbreak was not so severe as in former years. But I 
began to ask myself what there was about epidemic waves 
that made restrictive measures of little use, and also to inquire 
if there was anything wrong about the restrictive measures. 
If we were limiting these diseases at all, it was certainly in a 
very moderate way. 



LIMITATIONS TO THE VALUE OF ISOLATION 95 

Infection by Air and Fomites Thought Most Important. — 

It was fully appreciated that in cities at least most cases 
of contagious disease cannot be traced to their source. Two 
theories have from antiquity been advanced in explanation. 
One is that most contagious diseases are easily carried 
by the atmosphere. Thus a person going by a house where 
there is scarlet fever, or passing an infected person in the 
street, might contract the disease. Such unconscious exposure 
might be quite common. But the principal source of the 
untraced cases of contagious disease was believed to be fo- 
mites. Walls and furniture were thought to become infected 
with the virus, and for weeks and months persons entering 
the room might contract disease through the breath. Books, 
toys, clothing and, in fact, every material thing, might readily 
become a source of infection and retain its virulence for 
months and years. These were perhaps not unreasonable 
a priori hypotheses, and they had some apparent backing of 
facts. At any rate they were the best theories we had. So 
health officers everywhere, including Providence, set about 
improving methods of disinfection. Sulphur fumigation was 
abandoned and the use of formaldehyde gas adopted in 
its place. Many cities set up a steam disinfecting plant, in 
Providence as early as 1887, and carpets, bedding and cloth- 
ing were disinfected by steam. Some cities, particularly on 
the continent of Europe, sent a band of uniformed disinfec- 
tors to wash and scrub everything in the infected house. 
Scarlet fever and diphtheria refused to be exterminated, 
though in Providence we did have rather less during the early 
nineties than we had had before. But I was not satisfied. 
It seemed to me that we were having too much of these 
diseases, that there must be a leak somewhere. 

Cultures Expected to Discover Much Diphtheria. — Then 
for one disease a new weapon was put into our hands. Many 
had long recognized that the diagnosis of diphtheria was diffi- 
cult. It was suspected that many cases, because of this diffi- 
culty, escaped isolation entirely. When the culture method 



96 THE SOURCES AND MODES OF INFECTION 

of diagnosis was devised I became enthusiastic and hopeful. 
We adopted it in Providence in January, 1895, and soon after 
required a negative culture before the patient was released 
from isolation. Hill has shown that without cultures the 
chance of error in the diagnosis of diphtheria is 50 per cent, 
which corresponds entirely with my frequently expressed 
opinion before the advent of the culture method. It is evi- 
dent, then, that the general use of cultures ought to bring to 
light great numbers of cases of diphtheria which were formerly 
unrecognized, and this it certainly does. If such an im- 
provement in diagnosis, and consequently in isolation, is 
brought about by the use of cultures, and if by the same means 
isolation can be maintained until the patient is certainly free 
from infection, there ought to follow a marked reduction 
in this disease. But it was quite otherwise. The deaths in 
Providence, which in 1894 had numbered 45, rose to 79 in 
1895 and 125 in 1896, nearly twice as many in proportion to 
the population as there were in 1883, when there was no isola- 
tion, no disinfection and no antitoxin. The cases rose from 
166 in 1894 to 386 in 1895 and 890 in 1896. The apparent 
reduction in the fatality rate from 27.71 to 14.07 indicates 
very plainly that the culture method of diagnosis had dis- 
covered a very large number of mild cases that would have 
previously been unrecognized, for antitoxin was only a minor 
factor in reducing the fatality, as it had been used in only a 
little over one-third of the cases. Isolation, disinfection, the 
use of cultures, and the opening of the contagious hospital 
had been accompanied by the greatest prevalence of the dis- 
ease for ten years. I do not mean to say that the adoption 
of the measures described had no effect upon the amount 
of diphtheria in Providence. I am sure that they had, and 
that this disease on the whole has been lessened, cases pre- 
vented and lives saved. But better results were expected. 
I was disappointed, and I think other health officers have 
been disappointed also. It seemed that the measures, car- 
ried out as they were, ought to have given better results. 



LIMITATIONS TO THE VALUE OF ISOLATION 97 

It seemed that there was something which we did not 
understand. 

Failure of Hospital Isolation. — One of the most effectual 
means of isolating cases of contagious diseases is by removal 
to the hospital. Certainly while in the hospital they can do 
no harm, and with reasonable care there is not much danger 
of their carrying infection back to their homes. Return cases 
do not occur in scarlet fever and diphtheria in more than 
about one to three per cent of discharges, and are not a factor 
of moment in the extension of these diseases. The idea that 
such hospitals would be a powerful factor in the extermina- 
tion of these diseases was not unreasonable. Smallpox hos- 
pitals have been in general use for a very long time, but they 
are not here under consideration, though it is questionable 
whether the hospital isolation of smallpox can ever accom- 
plish much alone and unaided by vaccination. But it is the 
hospitalization of scarlet fever and diphtheria that is par- 
ticularly instructive. 

English Hospitals. — The use of hospitals for contagious 
diseases has been carried farther in England than elsewhere. 
Fifteen or twenty years ago the larger municipalities began 
building them on a considerable scale, and at present most 
of the English towns are provided with large hospitals for 
scarlet fever, and to a less extent for diphtheria. At the time 
when their construction was first strongly urged it was be- 
lieved that their use would result in the eradication of the 
diseases for which they were provided. The result has cer- 
tainly been disappointing, and there has recently been an 
active discussion as to whether they do an amount of good in 
restricting disease at all commensurate with their cost. 1 There 
is no doubt that the mortality from scarlet fever, both in 

1 O'Connor, Geo. Wilson, Waddy and others, Brit. M. J., Lond., 1905, 
II, 630; Millard, Biss, Fraser, etc., Med. Press & Circ., Lond., 1904, 
LXXVIII, 215, 218, 241, 327, 377; Newsholme, Tr. Epidem. Soc. 
Lond., n. s., 1900-01, XX, 48; J. Hyg., 1901, I, 145; Millard, Pub. 
Health, 1901, XIII; J. T. Wilson, Pub. Health, 1896-97, IX, Sup., p. 21. 



98 THE SOURCES AND MODES OF INFECTION 

England and the United States, has greatly diminished during 
recent years, but whether this has been due to restrictive 
measures or to lowered virulence has been disputed. The 
small death rate would indicate that the disease is really 
milder. This is also indicated by the fact that plural deaths, 
that is, more than one death in a family, are less frequent 
now than formerly. Again, local outbreaks of the old-time 
severe type occasionally appear. There was such an out- 
break in Providence in 1906-07, during which the case fatal- 
ity ran up to 12.85 per cent. Similar outbreaks have been 
noted in Keene, N. H., Haverhill, Worcester and Mont- 
real. The relatively lowered fatality in recent years has 
rendered it difficult to determine from the number of deaths 
just what influence restrictive measures, like hospital isola- 
tion, have had on the prevalence of scarlet fever, and increas- 
ing accuracy and care in reporting cases render it difficult 
to draw conclusions from the number of cases. But after 
all has been said it is clear that hospital isolation in scarlet 
fever has checked the disease very much less than was ex- 
pected, and sometimes appears to have had little effect. In 
Huddersfield, a city of nearly one hundred thousand people, 
from 1890 to 1899 the percentage of removals to the hospital 
was 90, yet the mean attack rate for the period was 4.3 per 
thousand. From 1900 to 1908 the removals to the hospital 
were 92.4 per cent and the attack rate 2.96. This is certainly 
a surprisingly high morbidity rate for a city where practically 
all reported cases have for twenty years been subjected to 
most excellent isolation. A similar state of things is noted 
in other cities. Some cities with a high per cent of removals 
to the hospital have more of the disease than do cities with 
no hospitals. The same is noted in rural communities. 
O'Connor, 1 medical officer of health of Leicestershire and Rut- 
land combined sanitary districts, reported that in five par- 
ishes where the percentage of hospital isolation had for ten 
years reached 66 per cent, the attack rate was 6.2 per thou- 
1 O'Connor, Brit. M. J., Lond., 1905, II, 630. 



LIMITATIONS TO THE VALUE OF ISOLATION 99 

sand, while in five other parishes where hospital isolation was 
applied to only 14 per cent of the cases, the attack rate was 
2.8. In another district, one parish which sent 60 per cent of 
its scarlet fever to the hospital, had three times as many 
cases as contiguous parishes which had little hospital isola- 
tion. Neech 1 says that in Cornwall from 1898 to 1907 there 
was practically no difference in the incidence of scarlet fever, 
in both urban and rural districts, connected with the use or 
failure to use isolation hospitals. Again, a city after it builds a 
hospital may have more of the disease than before. The aban- 
donment of hospital isolation may do no harm. In Leices- 
ter 2 the hospital was closed temporarily, and all the scarlet 
fever cases sent to their homes, with an actual decrease in 
number of reported cases. The hospital in other cities also 
has been closed without harm. I have thought it possible 
that at times hospital isolation might actually favor the 
spread of disease. When a case is removed to the hospital, 
comparatively little restraint is placed upon other members 
of the family, and if some of them are carriers, as they cer- 
tainly usually are in diphtheria, much harm may result. If, 
however, the case is kept at home, the rest of the family, 
particularly the children, are under considerable restraint for 
several weeks. Observations in Providence demonstrate that 
the retention of the case at home very rarely leads to the 
extension of the disease to other families in the house, and 
presumably to still less extension outside of the house. 

Why the Failure ? — It may be admitted, and is doubtless 
true, that hospitals have prevented very many cases of dis- 
ease, and they may have been somewhat of a factor in its 
lessened prevalence. Nevertheless it must also be admitted 
that, notwithstanding the complete and excellent isolation 
secured in some cities like Huddersfield, scarlet fever has 
still prevailed to an alarming extent. When eighty to ninety 
per cent of the cases are removed to the hospital it is certain 

1 Neech, Pub. Health, Lond., 1908-09, XXII, 296. 

2 Rep. on Health of Leicester, 1902, 36. 



100 THE SOURCES AND MODES OF INFECTION 

that the remainder will be so situated that home isolation will 
quite effectually prevent extension from them. In such cities 
almost all of the reported cases are thus effectively isolated, 
either in hospital or home. Yet the disease continues to pre- 
vail. There is evidently some source which escapes control. 
Newsholme has very clearly shown this. While admitting 
that isolation does prevent much sickness, he says that the 
disease still prevails and outbreaks still occur owing to some 
" epidemic influence." Now our purpose is to determine, if 
possible, what this " epidemic influence" is. What is the 
factor which is so powerful and continuous in its action that 
90 to 95 per cent of perfection in the isolation of a contagious 
disease is unable to prevent a continued high prevalence and 
repeated epidemic waves ? 

American Hospital Experience. — It is not merety English 
hospital experience which has shown the inefficiency of isola- 
tion. We have numerous instances in our own country. I 
have already referred to the experience of Providence, where 
increasing stringency in isolation was not followed by a 
decrease in contagious diseases. There has been much dif- 
ference between American cities as regards the strictness of 
enforced isolation. Some have been notoriously lax, while 
others have for years endeavored to secure a complete regis- 
tration of scarlet fever and diphtheria, and have adopted 
rigorous measures of isolation and disinfection, though in no 
American city has hospitalization been carried so far as it has 
in many English towns. But no one would be able, by study- 
ing mortality rates, to pick out the cities which pursue a 
rigorous policy of isolation. I collected data relating to the 
prevalence of scarlet fever and diphtheria in American cities 
for the decade 1890-1 899, x and it is surprising to note that 
the cities with the best sanitary administration frequently 
have a comparatively large amount of scarlet fever and diph- 
theria. During the period mentioned, Boston, in my opinion, 
had the best sanitary administration of any of the large cities, 

1 Chapin, Municipal Sanitation, Providence, 1901, Table op. 480. 



LIMITATIONS TO THE VALUE OF ISOLATION 101 

though New York stood high. The death rate from diph- 
theria in both cities was 84 per 100,000 living, from scarlet 
fever 25 for Boston, and 33 for New York. Certainly neither 
Chicago nor Cincinnati enforced such rigorous measures, yet 
the rates in these two cities were 72 and 71 for diphtheria 
and 17 and 7 for scarlet fever. Among the smaller Mas- 
sachusetts cities Fall River has usually had a rather ineffi- 
cient health service and little hospitalization, yet the death 
rate from diphtheria was 21 and from scarlet fever 15 per 
100,000 living, while in Worcester the figures were 48 and 8, 
and this notwithstanding the fact that in Fall River the 
proportion of children is much greater than in most Amer- 
ican cities, and that the population is exceptionally ignorant 
as measured by illiteracy. Worcester has had a contagious- 
disease hospital since 1897, and has removed to it in some 
years as high as 63 per cent of its diphtheria cases. In general, 
Worcester secures an excellent registration of cases, and con- 
sequent isolation. Nevertheless Worcester has recently had, 
notwithstanding its increasing hospitalization and good home 
isolation, a severe outbreak of the disease. It seems a fair 
assumption that some factor much more important than the 
recognized cases of the disease has been at work in Worcester. 
If it were not so, the reported cases of the disease should not 
have risen from 132 in 1905 to 1178 in 1907. 

Diphtheria Isolation at Home. — In Providence for some 
years previous to March, 1902, isolation in diphtheria was 
terminated only when a negative culture had been obtained 
from the patient. At that date a change was made, terminat- 
ing isolation ten days after the disappearance of exudation. 
This certainly liberated many cases still infectious, but this 
factor was of so little moment that the disease continued to 
decrease until on a certain day in August the city was entirely 
free from reported cases, a condition again nearly reached in 
1907. 

Isolation in Institutions. — It is by no means uncommon 
to see outbreaks in institutions lasting many months, al- 



102 THE SOURCES AND MODES OF INFECTION 

though every case is promptly isolated and all persons in the 
institution are repeatedly examined by cultures from throat 
and nose. I have records of several such in Providence, and 
most health officers and managers of institutions have been 
through such unpleasant experiences. Here again we are 
forced to look for sources other than the recognizable cases. 

At a school in Owatonna, Minnesota, 1 there had been more 
or less diphtheria for years until a sharp outbreak in 1896 
caused a very energetic effort to be made to stamp it out. 
Cultures were taken from everybody, and all persons in whom 
diphtheria bacilli were found were isolated, at first in a com- 
mon ward, but later each person in a separate room. Isola- 
tion was maintained until three successive negative cultures 
were obtained from throat and nose, and efficient disinfection 
was practiced. Still the disease persisted month after month, 
and some of the carriers, after release, were found to be still 
harboring the bacilli. One boy carried the bacilli for nineteen 
months. The attempt at the isolation of carriers was aban- 
doned, and several years later there was still more or less 
diphtheria in the institution. 

A still more notable failure of the isolation of diphtheria 
was at the Willard State Hospital for the insane in New York. 2 
In this institution practically the same methods were adopted 
as at Owatonna, but nevertheless the disease persisted sev- 
eral years. Patients and carriers released from isolation after 
several negative cultures were still found to be carriers. If 
in an institution of this kind, where the strictest discipline 
is maintained, and where carriers can be isolated indefinitely, 
the most stringent measures of isolation and disinfection fail 
to stamp out the disease, what is to be expected of any such 
measures which can be adopted in an ordinary community? 

An outbreak in a hospital in California was managed in 

1 St. Paul M. J., 1900, II, 223; Brit. M. J., Lond., 1898, I, 1008; Rep. 
St. Bd. Health, Minnesota, 1897-98, 465; Rep. Am. Pub. Health Ass., 
1899, XXV, 546. 

2 Rep. State Commission in Lunacy, N. Y., 1904, XVI. 



LIMITATIONS TO THE VALUE OF ISOLATION 103 

the same way. 1 At first no effect seemed to be produced, 
and the outbreak lasted from April to August, but was as- 
sumed to have been finally checked by the same measures 
which failed at Owatonna and Willard. But as many out- 
breaks last even a shorter time, though no attention is paid 
to carriers, it is uncertain whether the outbreak was stamped 
out or died out. Sidney Davies 2 reports that at the Bostall- 
lane School in Woolwich diphtheria prevailed for three years 
notwithstanding repeated closures and bacterial examinations 
of the pupils. There is little doubt that at times a careful 
search for carriers and missed cases in schools and institu- 
tions and their isolation until two successive negative cul- 
tures from throat and nose are obtained, prove successful in 
checking outbreaks; there is no doubt, too, that outbreaks 
frequently die out of themselves; and it is shown by the exam- 
ples given above that it is at times impossible by any degree 
of isolation to stamp out an outbreak. How to manage such 
institutional epidemics cannot be determined until the con- 
trol of carriers is more carefully studied than it has been. 

Isolation a Failure in Measles. — Measles is a disease 
which in cities it seems to be impossible to check to any 
appreciable extent by isolation. In Aberdeen 3 this was faith- 
fully tried for twenty years, 1883 to 1902, but no apparent 
effect was produced on the prevalence of the disease. Similar 
failures have been noted elsewhere. During the last half of 
this period in Aberdeen, when there was far more accurate 
registration and better control than before, the number of 
cases rose to 24,254, about fifty per cent more than in the first 
half of the period. A census of the children in certain schools 
indicated that from ninety to ninety-three per cent of children 
over ten years of age had had the disease. Restrictive meas- 
ures which protected only seven to ten per cent of the popu- 
lation from attack were then wisely abandoned. The very 

1 Rep. State Bd. of Health, California, 1906-08, 201. 

2 Rep. Med. Off. Health, Lond., 1908, 36. 

3 Aberdeen, Report of Med. Off. of Health, 1904, 41. 



104 THE SOURCES AND MODES OF INFECTION 

excellent report of the medical officer of health of Aberdeen 
discusses the subject very fully. In New York measles was 
first isolated in 1896, but not until 1902 were the regulations 
very rigorously enforced. The average death rate from 1895 
to 1904 was 2.40, and the highest death rate since 1896 was 
reached in 1906, when it was 2.69. There is no evidence that 
the measures adopted in New York have had any more 
influence on the prevalence of the disease than did isolation 
and disinfection in Aberdeen. It seems in the highest degree 
probable that the disease prevails because of the unrecognized 
but infectious prodromal stage. No amount of isolation after 
the disease is recognized can atone for the harm done before 
the diagnosis is made. 

Isolation a Failure in Meningitis. — Within a recent period 
the city of New York suffered from an exceptionally long and 
severe outbreak of cerebro-spinal meningitis. The attack 
rate was higher than in any of the other large American cities, 
and the outbreak lasted longer; and it lasted longer than it 
has in most of the German cities. On April 19, 1905, after 
the epidemic had continued for about two years, very strin- 
gent restrictive measures of isolation and disinfection were 
adopted. The outbreak was then declining, and that it would 
afterwards decline still more was to have been expected. 
But it was not " stamped out," for in 1907 there were reported 
642 deaths and in 1908, 351. In Leith * great efforts 
were made to isolate all suspects and carriers, and the 
outbreak appeared to be checked, but in Edinburgh also 
it died out, though without such energetic measures. The 
experience in Germany seems to be that if in the beginning 
diligent search is made for carriers, and strict isolation is 
maintained, the outbreak may sometimes be checked, but 
after the disease has become established, and carriers are 
numerous, isolation is of little avail. These appear to be 
the views of Lingelsheim, Ostermann, Selter, Flatten and 
others. 

1 Ker. Practitioner, Lond., 1908, LXXX, 66. 



LIMITATIONS TO THE VALUE OF ISOLATION 105 

Isolation often a Failure in Smallpox. — Smallpox is less 
likely to escape detection than is any other disease. Yet 
epidemics grow in the face of the most rigid isolation. Unrec- 
ognized cases, even in this disease, are so numerous that the 
isolation of the recognized cases often seems to be a complete 
failure. The State Board of Health of Minnesota, realiz- 
ing this, 1 has had the boldness to advise that no attempt be 
made to isolate, and that entire reliance be placed on vacci- 
nation. It was hoped that this would lead to more complete 
vaccination. There has been no alarming increase in small- 
pox in Minnesota, and Montana 2 is now following the lead 
of the former state. 

Why Does Isolation Fail ? — The epidemiological evidence 
is conclusive that the isolation of recognized cases of con- 
tagious diseases often fails to check outbreaks which grow 
in spite of it; that it does not stamp out disease, and that it 
only reduces in a moderate degree the prevalence of the 
disease. We are forced to conclude that there is some defect 
in our procedures, or some other source of infection more 
important than the recognized cases. The error cannot be 
that isolation is too brief, for return cases and recurrences 
are not important factors. It is not that isolation is imper- 
fect, for isolation in the hospital is well-nigh complete, and 
careful observations in Providence indicate that the danger 
of extension outside the family from cases at home is very 
slight. 

Importance of Carriers and Missed Cases. — As has been 
previously stated, two theories have been advanced to account 
for the appearance of untraced cases of contagious diseases: 
that of distant aerial infection, and that of the persistence of 
infection on things, i.e., fomites. In other chapters of this 
book it is shown that both of these modes of infection are 
of little moment, and in the first chapter it was shown to be 

1 Resolution adopted July, 1906, to go into effect January, 1908, 
Am. J. Pub. Hyg., 1907, III, 227. 

2 Am. J. Pub. Hyg., 1909, V, 815. 



106 THE SOURCES AND MODES OF INFECTION 

unlikely that the specific organisms of our common diseases 
grow outside of the body. In the second chapter it was 
shown that they may grow in the body and yet produce few 
or no symptoms. It appears, then, highly probable that by 
far the most important factor in the causation of the con- 
tagious diseases are the "carrier" and " missed" cases. 

It is not for a moment suggested that the existence of 
carriers explains all epidemiological problems. There are, for 
instance, quite a number of contagious diseases which exhibit 
a varying degree of periodicity. We have as yet only the 
vaguest notions as to the causes of the variations in the 
prevalence of disease, its seasonal irregularities, and the rise 
and fall of epidemics. There is no reason to believe that 
these phenomena depend on the extra-corporal growth of 
pathogenic organisms, and it is probable that the seasonal 
distribution of such diseases as smallpox and scarlet fever is 
only in the most indirect manner dependent upon tempera- 
ture, rainfall, etc. It is not unlikely that the factors affecting 
the extension of these diseases are so numerous that their 
prevalence is really to a large extent a matter of chance. 
But whatever the factors may be, we must believe that they 
affect carriers as well as clinical cases. Why we have more 
carriers and more cases at one time than another, we cannot 
at present say. But it appears to be in the highest degree 
probable that in times of outbreaks, as well as in inter- 
epidemic periods, the chief factor in the extension of the 
disease is the existence of unrecognized infection in human 
beings or, in some diseases, in the lower animals. 

Need of Further Study. — I would be the last person to 
assert that the views here set forth are unassailable and unal- 
terable. They doubtless will be modified; it may be that 
they are entirely erroneous. What is needed is further inves- 
tigation along the lines indicated, and a great deal of it. 
Unfortunately sanitary science is far from exact. We have 
few established truths, but many theories of greater or less 
probability, on which to base our practice. The probability 



LIMITATIONS TO THE VALUE OF ISOLATION 107 

of each theory must be carefully weighed. Which is the most 
probable source of infection, the cesspool in the yard, the 
fomites that escaped disinfection, the patient who was re- 
leased too soon, or the unknown carrier ? The chances are 
greatly in favor of the last, and yet to-day sanitary practice 
almost completely ignores the carrier. It is not surprising 
that many health officers fail to appreciate the importance 
of the question which is here discussed. It is remarkable, 
however, that bacteriologists as a rule minimize the danger 
to be apprehended from carriers. 

Carriers not to be Ignored. — It may be admitted that 
only 1 per cent of the population are diphtheria carriers, 
though as a matter of fact it must often be more than that; 
also that only 15 per cent of these carry virulent germs, though 
it is really often much greater. It may also be admitted that 
these bacilli are not usually so numerous as in the sick, though 
it is known that they sometimes appear in pure culture; yet 
even admitting all this, there will be in inter-epidemic periods 
in a city of 100,000 people at least 150 well persons carrying 
virulent diphtheria bacilli. Why should the bacteriologist 
ignore these 150 sources of infection and insist on two throat 
and nose negative cultures from every reported patient ? Or 
why should he, as he occasionally does, recommend isolating 
the carriers in the family but ignore all other carriers ? Why 
neglect this whole question of carriers, and spend endless time 
in devising methods of liberating formaldehyde to kill the 
few bacilli that may remain about the house ? Why worry 
about the saliva that may have gotten onto a book, a coat, 
or the wall of a room, and neglect the reader of the book, 
the wearer of the coat and the dweller in the room, who is 
probably growing the germs in his throat and nose ? It is 
not easy to answer these questions, and so the bacteriologist 
withdraws to his laboratory and ingores them. But the 
health officer must answer them in one way or another. 

Principles of Diphtheria Isolation. — To confine the dis- 
cussion for the moment to diphtheria, concerning which we 



108 THE SOURCES AND MODES OF INFECTION 

have more accurate knowledge than we have for any other 
disease, there appear to be only two logical positions which 
the health officer can take in regard to its management. 
There is the possible policy of non-regulation. This the public 
would certainly not permit, and I think with very good 
reason. Or we can go to the other extreme and attempt to 
isolate every person carrying diphtheria bacilli, until they 
disappear from throat and nose, or until they are shown to be 
non-virulent. That is, of course, entirely impracticable except 
in small isolated communities or institutions, and it is often 
very difficult, and sometimes impossible then. In every large 
city there are hundreds of carriers who can never be detected, 
and who could not be controlled if they were. Virulent bacilli 
may remain for months, and the attempt to isolate for a pro- 
longed period prominent lawyers, business men, or physi- 
cians, would result in a breakdown of the whole system. 
As a matter of fact, such carriers escape from isolation while 
still infected. If cultures are taken daily, or every few days, 
it is usually not very long before the two negatives required 
by rule are secured and the patient is released, though sub- 
sequent cultures not infrequently reveal the bacillus. The 
ideal of health officers has been to keep up isolation until 
every spark of infection has died out, — a very reasonable 
ideal, until it was learned that there are many hidden sparks 
scattered about the community, some of which are sure sooner 
or later to burst into flame. As it is impossible to attain the 
ideal of stamping out all infection, and as it is certain that 
many infected persons cannot be restrained at all, it is unrea- 
sonable to require restraint to the uttermost limit, of the 
recognized cases. It is often argued that the fact that all 
infected persons cannot be isolated, is no reason for not iso- 
lating all that can be found, anymore than the fact that many 
thieves escape is no reason for not imprisoning those thieves 
who are caught. But there is no true parallel here. The 
thief is a criminal, and his imprisonment is a punishment. 
The bacillus carrier is not a criminal, and he is isolated, not 



LIMITATIONS TO THE VALUE OF ISOLATION 109 

as a punishment, but to protect the community. If the 
protection secured is not commensurate with the hardship 
inflicted, the procedure is unjust, and unwise from a socio- 
logical standpoint. 

A Compromise Necessary. — But just as soon as we depart 
from the orthodox ideal, absolute isolation, we have to adopt 
some sort of compromise, a compromise which has no strictly 
logical defense. We are thus forced to follow one of three 
policies, — either do nothing, which is unwise and would not 
be permitted, or attempt absolute isolation of all sources 
of infection, which is manifestly impossible, or employ a 
moderate degree of restriction, which, though not strictly 
logical, is nevertheless practicable, reasonable and to a con- 
siderable degree effective. 

Isolation of Real Value. — While the most rigorous isola- 
tion does not stamp out diphtheria, we know that restriction 
does some good. The removal of a case to the hospital is 
shown by statistical evidence to prevent to some extent the 
development of secondary cases in the family. So too does 
good isolation at home. The warning sign on the house 
keeps out many people, some of whom would otherwise cer- 
tainly contract the disease. The regulation of school attend- 
ance prevents some school outbreaks, and others are checked 
by the prompt removal of the infecting child. The evidence 
points to an appreciable reduction in diphtheria prevalence 
in recent times, which I believe it is fair to consider as due, 
in part at least, to deliberate separation of the sick from the 
well under the direction of the sanitary authority or other- 
wise. Why more has not been accomplished by isolation is 
explained by the facts set forth in the preceding chapter. 
If because of the existence of so many unrecognized sources 
of infection, isolation can effect only a limited degree of pre- 
vention, could not substantially as much be accomplished 
by more moderate methods than are usually employed ? 
Why keep the patient indoors for six weeks when other mem- 
bers of the family with infected throats are going about ? 



110 THE SOURCES AND MODES OF INFECTION 

Why keep from work the wage earners in an infected family 
when scores of other carriers are attending to their business 
without restraint ? 

Typhoid Carriers cannot be Isolated. — The isolation of 
typhoid carriers is no more possible, just, or effectual in check- 
ing disease, than is the isolation of diphtheria carriers. As 
was shown in the preceding chapter, the number of carriers 
and convalescents excreting bacilli is probably much larger 
than the number of cases confined indoors. It seems to me 
useless to attempt to confine convalescents two or three 
months after their recovery. There certainly would be most 
energetic opposition on the part of the public, which probably 
would ultimately be sustained by the courts. The health 
officer who attempted to isolate convalescents until bacilli 
were no longer to be found in their urine, would be in an 
awkward position if he allowed chronic carriers to go at large, 
and he would be in a still more awkward position if he at- 
tempted to isolate all chronic carriers indefinitely. There 
are probably 200,000 cases of typhoid fever in the United 
States each year, and 3 per cent of these would be 6,000. 
To attempt to isolate 6,000 carriers would of course be futile. 
Not one-tenth of them could even be discovered. To isolate 
the small fraction of carriers who can be discovered is practi- 
cally useless, and therefore unjust. It may be, and probably 
is, wise to regulate the life of such carriers as may be dis- 
covered, and at times to forbid their engaging in certain 
occupations, such as those of cook, waitress and milk dealer, 
but to attempt their isolation under present conditions seems 
to me most unwise. 

Isolation too Rigorous. — I believe that, on the whole, iso- 
lation in our prevailing contagious diseases is carried farther 
than is necessary; that less rigorous measures would accom- 
plish practically as much good, and that there would be less 
temptation to conceal cases and to interpret doubtful symp- 
toms in line with the patient's desires. It is impossible here 
to lay down in detail a scheme for the proper isolation of 



LIMITATIONS TO THE VALUE OF ISOLATION 111 

contagious diseases. What are the best methods of dealing 
with these diseases is a matter for free discussion, and also 
for experiment. It is to call attention to the new facts, and 
to elicit discussion from the new viewpoints, that these pages 
are written. 

Degree of Contagiousness. — Before considering some of 
the principles which should guide the application of meas- 
ures of isolation, we should consider what are, under the 
ordinary conditions of life, the chances of infection from a 
single individual. Until recently it has been believed to be 
very great. That smallpox hospitals are placed a mile or 
more from inhabited districts, that physicians clothe them- 
selves with gowns and caps and rubber boots on their visits 
to infectious cases, and that it is insisted that the ceiling of 
a room occupied by such a case be disinfected, indicate a 
belief that the virus of the contagious diseases is exceedingly 
diffusive and exceedingly virulent. Why such a belief is not 
well founded will be shown in succeeding chapters, and it 
will suffice here to call attention to the fact that the chance 
of an infected person transmitting the infection to another 
is not nearly so great as is generally supposed. This is a 
mathematical necessity. We now know that the number of 
infected persons is very much greater than was formerly 
believed, and that they often remain infected for much longer 
periods than was suspected. It necessarily follows that the 
danger to be apprehended from any one person at any one 
time is much less than was once thought. 

Factors Involved. — The chance of an infected person giv- 
ing rise to the disease, or of transmitting the infection to 
others, varies greatly with the intensity of the infection, or 
the number of disease germs in the secretions or excre- 
tions, their virulence, the volume of the excretions, the care 
exercised, the occupation, and the surroundings generally. 
Conditions in the home and in institutions are usually much 
more favorable than elsewhere for the transmission of infec- 
tion. Yet in the home the chance of such extension of disease 



112 THE SOURCES AND MODES OF INFECTION 

is not as great as has been supposed. In Providence, 1 the 
chance of persons contracting diphtheria from another mem- 
ber of the family who has the disease is only about 1 in 15. 
The chance of a child between two and six years contract- 
ing it is 1 in 5; of an adult, 1 in 40. The chance of a woman 
contracting the disease in the family is about three times as 
great as that of a man. For scarlet fever the figures are 
not very different. Every one must have noted repeated 
instances where only one of a family of children is attacked 
by scarlet fever or diphtheria, the rest of the family remaining 
well, though isolation may have been far from satisfactory. 
Danger Less outside Family. — Outside of the family, in 
school, in factory and in ordinary social relations, except per- 
haps in the play of young children, the chance of transmitting 
the disease must be very much less. Instances are not rare 
where children, presumably in the infectious stage of scarlet 
fever, have mingled freely with others for many days, or 
perhaps weeks, with little or no extension of the disease. I 
have notes of an instance where a boy with scarlet fever in 
the sore-throat stage attended a Sunday-school festival, and 
no other case developed among the large number of children 
present. At an infant asylum a child was sick with mild 
scarlet fever for 17 days, mingling freely with about 75 chil- 
dren, mostly under 5 years of age, and only 3 other cases re- 
sulted. At a large school a girl returned at the end of the 
first week of an attack of scarlet fever, and continued her 
attendance for 20 days. Only 3 or 4 cases developed in that 
school. Similar and even more marked instances of appar- 
ently feeble infectivity are reported by others. I have made 
no attempt to collect such cases, but I happen to have before 
me three reported by Butler. 2 One child, taken sick Novem- 
ber 5, attended school from November 11 to November 19. 
Two other children, attacked December 26 and 27 respec- 
tively, attended different schools up to January 16. In only 

1 Rep. Supt. of Health, Providence, 1909. 

2 Butler, Proc. Roy. Soc. Med., Lond., 1908, I, Epidemiol. Sec., 225. 



LIMITATIONS TO THE VALUE OF ISOLATION 118 

one of the three schools did even a single case occur. I have 
known of a teacher with virulent diphtheria bacilli in her 
throat from the first of January to the middle of April, who 
taught in a kindergarten all that time, but who did not trans- 
mit the disease to any one. Many of the instances of typhoid 
carriers which have been referred to, show that such persons 
may for long periods of time fail to infect any one, even though 
employed as cooks or handlers of milk. I have known of 
cases of smallpox remaining for several days in lodging 
houses or hospital wards, or traveling on railroads, without 
any one contracting the disease. Failure to infect may be 
due sometimes, perhaps, to intermittency in the excretion of 
germs, sometimes to lack of contact, and sometimes to lack 
of susceptibility on the part of the receiver of the infection. 
Whatever the cause may be, we must recognize that an 
infected person often mingles freely with the public without 
transmitting the infection to another. 

Carriers less Infective than the Sick. — As has been 
stated, it is not improbable that the infectivity of a well car- 
rier may for several reasons be less than that of a person sick 
with the disease. It may then be argued that the danger 
from carriers has in the preceding pages been very much 
exaggerated. It is not to be denied that the probable danger 
from a single carrier is small. Their number, however, is 
large, so that the danger from all carriers is large, and is, 
I believe, a very considerable factor in the maintenance of 
the contagious diseases. 

Isolation should Vary. — In applying isolation to the 
prevention of disease it must be kept in mind that different 
conditions require different procedures. Thus when an ordi- 
nary contagious disease first appears, after a considerable 
absence, in a small community, or in an institution, very 
rigorous measures of isolation are usually desirable, as expe- 
rience has shown that very often an outbreak is thus effec- 
tively checked in its beginning. 

Isolation in Villages. — The efficacy of isolation under such 



114 



THE SOURCES AND MODES OF INFECTION 



circumstances is well illustrated by the history of outbreaks 
of the common contagious diseases in the smaller cities, town- 
ships and villages of Michigan. The data given in the annual 
reports of the board of health of that state are of great epi- 
demiological interest, and my discussion of the subject on 
another occasion is here given. 1 

" Only those places are considered which have remained 
free from the disease for at least sixty days, and this unfor- 
tunately is never true of a city of any considerable size. The 
outbreaks reported are arranged in groups, one in which iso- 
lation and disinfection were both enforced, one in which they 
were both neglected, and one in which the reports did not 
state with sufficient exactness what restrictive measures were 
carried out. The following is a summary of some of the 
tables in the report: 





Number of Cases 
per Outbreak. 




Number of Cases 
per Outbreak. 




Restric- 
tive Meas- 
ures not 
Enforced. 


Restric- 
tive 
Meas- 
ures 
En- 
forced. 


Restric- 
tive Meas- 
ures not 
Enforced. 


Restric- 
tive 
Measures 
Enforced. 


Typhoid fever, 10 years . . 

Diphtheria, 14 years 

Scarlet fever, 14 years .... 

Measles^ 11 years 

Smallpox 


5.82 
11.12 
11.95 
48.30 


3.13 
2.11 

2.32 
3.03 


1900 


6.72 

4.85 

10.43 

27.60 

32.00 


2.22 
1.71 
2.53 
4.67 
3.80 











Isolation Effective. — " Several things are to be noted in 
connection with these figures. In the first place, isolation 
and disinfection accomplish very much in preventing the 
extension of all these diseases. The number of facts is so 
great, the outbreaks of each disease running into the hun- 
dreds, and the difference between good and bad sanitation is 
so manifest in each one of the years for each one of the 

1 J. Mass. Ass. Bds. Health, Boat., 1904, XIV, 226. 






LIMITATIONS TO THE VALUE OF ISOLATION 115 

diseases, that the success achieved must be a very real one. 
It appears certain that isolation and disinfection as practiced 
in the smaller communities of Michigan reduce the cases of 
contagious disease in round numbers from forty-five to ninety- 
five per cent. In scarlet fever, diphtheria, measles and small- 
pox, isolation appears from the reports, as one would expect, 
to have very much more restrictive effect than disinfection. 

"As will be shown later, disinfection probably has little 
influence in restricting contagious diseases, but in view of 
existing ideas and practices it is probable that isolation and 
disinfection were not so distinctly separable as is indicated by 
the reports of the local health officers. One of the things 
which appeared most remarkable to the writer in these re- 
ports is the apparently great restriction of measles. It has 
certainly been the experience in all our larger cities that 
restrictive measures, no matter how energetic, have had very 
little effect in reducing the mortality from this disease. But 
in the smaller communities in Michigan it appears that where 
isolation and disinfection are well carried out there is nearly 
ninety-four per cent less cases per outbreak than where pre- 
cautions are neglected. 

Cause of Success. — " But if one examines the original 
returns of the health officers it appears plain why such good 
results are obtained. If the first case of the disease coming 
to a community is early recognized and isolated the chances 
are good that the outbreak will be at once checked. The 
chances that such a case will be so recognized in a village are 
very much greater than in a city. If, however, the outbreak 
is not checked at its very outset, the chances are, even in the 
country, that its extension will be very considerable. As a 
matter of fact, a great many of the first cases coming to small 
communities are promptly recognized and isolated, and as a 
result an outbreak is prevented. It is because outbreaks are 
in rural communities so often nipped in the bud that the 
application of restrictive measures in such communities makes 
such a good showing. What is true of measles is true also 



116 THE SOURCES AND MODES OF INFECTION 

of other diseases, particularly of scarlet fever and diphtheria. 
It is success in applying restrictive measures to the first case 
that is the principal cause of the apparent efficiency of these 
methods. If every appearance of contagious disease in these 
rural communities had gained some headway before restric- 
tive measures were applied, the showing would not be nearly 
so favorable. In fact, in the large cities in Michigan, where 
these diseases are always epidemic, restrictive measures, even 
of a very rigorous type, have not enabled the health officers 
to * stamp them out.' Thus in Detroit it was the custom 
for many years to ' quarantine' absolutely every house 
where there was scarlet fever or diphtheria. No one was 
allowed to go out, and the inspectors visited the house twice 
a day and furnished provisions for the poor at an expense 
of thousands of dollars annually. Yet these diseases were no 
more ' stamped out' in Detroit than they have been in 
Chicago or other cities where milder methods have prevailed." 

Isolation in Common Diseases. — When measles, diph- 
theria or scarlet fever appears in a town or institution which 
has for some time been free from the disease, the patient ought 
to be isolated until it is as certain as medical science can 
determine that he is free from infection. At least this should 
be attempted. If it should happen, as it sometimes does, 
that the diphtheria patient retains virulent bacilli for many 
months, or that the scarlet-fever patient has a discharging 
ear for a similar period, isolation will probably have to be 
abandoned. But isolation is worth trying, for in the majority 
of instances safety is secured in a few weeks. Contacts also 
should be carefully examined and isolated, or otherwise re- 
stricted as to their relations with the community. If after 
a reasonable time the disease is " stamped out " the health 
officer is to be congratulated. If it is not stamped out he 
may well temper the rigor of his restrictive measures. 

When a rare disease, as plague, leprosy, or cholera, appears 
in Europe or North America, equally stringent measures 
should be employed. At present smallpox belongs rather 



LIMITATIONS TO THE VALUE OF ISOLATION 117 

to this class of rare diseases, and strict isolation of the first 
case and careful examination and supervision of contacts is 
desirable and useful. 

Many Carriers make Isolation Useless. — The effective- 
ness of isolation, and the consequent reason for its practice, 
varies inversely as the number of carriers and missed cases. 
With the enormous number of carriers of pneumococci, it is 
entirely useless to enforce isolation of cases of pneumonia. 
Influenza belongs to the same class as pneumonia, in which 
compulsory isolation is useless. It is probable also that noth- 
ing which the health officer can do in the way of isolation 
will have any effect on the extent of outbreaks of cerebro- 
spinal meningitis. The enforced isolation of typhoid fever, 
owing to the number of carriers, will usually prove of little 
value. While it is probable that there are few carriers of 
measles, yet the long prodromal but extremely infectious 
stage renders ineffectual measures of restriction. If isolation 
of measles is attempted, little can be hoped for other than a 
slight postponement of the age of attack, and no measures 
should be adopted which inflict any great hardship. No one 
advocates the isolation, in the ordinary meaning of the term, 
of pulmonary tuberculosis. It is not attempted in this 
disease simply because infected persons are so numerous that 
it is impossible. If tuberculosis were as rare as leprosy, strict 
isolation would be, and should be, demanded. On the other 
hand, there are so few carriers of smallpox that, even with 
the mild type of the disease prevailing, strict isolation is often 
advisable. 

To discover the proportion of carriers to recognized cases, 
for each disease, is a matter of the greatest practical impor- 
tance. We must have a fairly clear idea of how many un- 
recognized human foci of infection there are before we can 
determine upon what methods of isolation, if any, are likely 
to prove effective. Yet the investigation of carriers has 
received comparatively little attention at the hands of 
bacteriologists. 



118 THE SOURCES AND MODES OF INFECTION 

Value of Hospitals. — Hospitals are useful for protecting 
the family, for checking outbreaks in institutions, for receiv- 
ing cases from lodging houses and hotels, for furnishing better 
medical service, and for relieving the overworked housewife 
in the families of the poor. It is an unnecessary expense 
to provide hospital accommodations for all cases of scarlet 
fever and diphtheria, or for ninety per cent or even eighty 
per cent. That half or two-thirds of the cases of these 
diseases can, for all practical purposes, be equally well cared 
for at home, is not unlikely. 

Home Isolation. — In home isolation of scarlet fever, diph- 
theria and measles, the patient should, for the benefit of the 
public, be kept in the house. It does not seem reasonable to 
prolong isolation until all possible chance of infection has 
ceased. Exactly what the period should be in each disease 
should now be a topic for renewed discussion. 

Isolation in Providence. — In Providence at present the 
period of isolation for scarlet fever is four weeks from the 
beginning of the case. Up to 1902 the period was five weeks. 
Since the reduction in the period of isolation, the attack rate 
has been about 33 per 100,000 living, although one of our 
largest epidemic waves occurred during this period, and regis- 
tration is certainly far better than formerly. From 1884 to 
1901 the attack rate was about 34 per 100,000. In diph- 
theria, isolation is maintained for ten days after the disap- 
pearance of the membrane. The decrease in the prevalence 
of the. disease which followed the adoption of less rigorous 
isolation has been previously alluded to. 

Family. — When the attempt is made to isolate the patient 
in the family from the family, in order to protect other mem- 
bers, the duration of isolation may well be left to the dis- 
cretion of the family. It is the duty of the health officer 
to explain that the longer the separation of sick from well 
is maintained, the more likely it is to be effective. In scarlet 
fever there is no means of determining when the patient is 
free from infection. I am in the habit of recommending 



LIMITATIONS TO THE VALUE OF ISOLATION 119 

separation from the family for six weeks, perhaps a somewhat 
shorter time if the case is a mild one, and longer if there is 
aural or nasal discharge. In Providence, scarlet-fever cases 
are usually sent home from the hospital in four or five weeks, 
if free from nose and ear discharge. No regard need be paid 
to desquamation, as the experience of English hospitals has 
shown that no danger is to be feared from that source. 1 It 
is absurd to isolate with strictness a diphtheria patient from 
the rest of the family unless cultures have shown that the 
rest of the family are free from the bacilli. If such home iso- 
lation is to be undertaken at all, it should be continued, if 
possible, until two or three successive negative cultures have 
been obtained. 

Hospital. — Diphtheria cases in Providence are usually in 
the hospital until two, three or four successive negative cul- 
tures from the throat have been secured, the greater precau- 
tion being taken when the child is to return to an institution. 
Sometimes the patient is sent out while still harboring bacilli. 
The duration of isolation of the living cases is 19.65 days, 
and the percentage of return cases has been 1.9. In London 2 
the period of detention of 6866 cases was 57.5 days, and the 
percentage of return cases was 1.2, about 0.5 per cent less 
than in Providence, although the period of detention was 
almost three times as long. The duration of stay in the Provi- 
dence hospital for scarlet fever, surviving cases, is 45.67 days, 
and the percentage of return cases is 3.4. In the London 
hospitals the period of detention is 64.9 days, 3 and the per- 
centage of return cases, 1902-04, was 3.22. 

1 Metropolitan Asylums Board Report on Return Cases of Scarlet 
Fever and Diphtheria, 1902-04, 6. See also my discussion of this subject 
in FiskeFund Essay LII, published by R. I. Medical Society, Providence, 
1909. 

2 Metropolitan Asylums Board Report on Return Cases of Scarlet 
Fever and Diphtheria, 1901-02, 59, 62. 

3 Metropolitan Asylums Board Report on Return Cases of Scarlet 
Fever and Diphtheria, 1902-04, 5, 23. 



120 THE SOURCES AND MODES OF INFECTION 

School. — School children in infected families should be 
excluded from school for a liberal period, for this works little 
hardship, and the state should make special effort to keep 
its schools free from disease. Yet school exclusion may be, 
and often is, carried to excess. In Providence children living 
in a family where there is scarlet fever are excluded from 
school for four weeks from the beginning of the last case. 
In all except the poorer class of houses children living in 
other families in the house are permitted to attend school. 
In diphtheria, children in the infected family are not allowed 
in school for four weeks, provided that if all the school chil- 
dren in the family yield two throat and nose negative cultures, 
they may attend school after the warning sign has been 
removed (which is ten days after the disappearance of the 
exudation). Children in other families in the better class of 
houses are admitted to school if one negative culture is ob- 
tained from throat and nose. After the expiration of a month, 
all children in families where there has been diphtheria are 
usually admitted to school whether or not they are carrying 
morphologically typical bacilli, and of course quite a number 
do go to school while infected. Doubtless these carriers may 
at times infect others in school, but even if two negative cul- 
tures were required before readmission, some children would 
probably still prove infectious. Absolute security is impos- 
sible, and the rule should be so framed as to accomplish a 
maximum amount of good with a minimum amount of an- 
noyance. 

Wage Earners. — There is little reason for excluding wage 
earners from their work except in a few occupations. Most 
of the carriers we cannot restrain, and therefore why penalize 
those who have the additional misfortune of sickness in their 
families ? 

The most dangerous carriers are those who handle milk; 
hence milk producers and dealers living in infected families 
should be excluded from work. Judging from the number 
of reported outbreaks, the danger is probably greater for 



LIMITATIONS TO THE VALUE OF ISOLATION 121 

typhoid fever than for any other disease. It is probably wise 
to regulate the occupation of all typhoid contacts who 
handle any kind of food that is eaten raw. Perhaps the same 
should be done with diphtheria contacts. Teachers and 
nurses may very properly be prevented from following their 
usual vocations if they live in infected families. It has been 
my custom also to exclude from work car conductors, post- 
men, barbers and department-store clerks. I doubt, however, 
whether this is always advisable. I am very sure that 
laborers, mill operatives and office clerks need not, under 
ordinary circumstances, be kept from their business. 

Summary. — As regards the employment of isolation for 
the prevention of the spread of infectious disease we may 
fairly conclude: 

1. The danger to be apprehended from a single infected 
person is much less than has been supposed. 

2. Isolation is of far less value than was believed a few 
years ago. 

3. The fewer the infected persons in any community or 
institution the more likely is isolation to be successful. Iso- 
lation in an extensive outbreak rarely accomplishes much. 

4. The effectiveness of isolation varies inversely as the 
number of missed cases and carriers. 

5. Hospitalization in such diseases as scarlet fever and 
diphtheria cannot be expected to exterminate them, and the 
majority of patients can be as well cared for in their homes. 

6. In diphtheria, scarlet fever and measles there is rarely, 
and only in certain occupations, any necessity for interfering 
with the freedom of the wage earners of the family. 

7. The isolation of school children should be more strict 
than that of adults, for less hardship results, and there is 
more danger in the mingling of children than in the inter- 
course of adults. 



CHAPTER IV. 

INFECTION BY CONTACT. 

Most Obvious Mode. — Contact infection is the most 
obvious mode of transmission of the infectious diseases. For 
the sick to touch the well, and thus infect them, seems to be 
the most natural way of accounting for the spread of these 
diseases. If contact infection can explain epidemiological 
phenomena, there is no occasion for assuming the growth of 
pathogenic germs outside of the body, or of infection by fo- 
mites or infection by air, or any other similar theory, and 
no such theory should be adopted as a working hypothesis 
unless pretty strong evidence can be brought to its support. 

Venereal Diseases. — Gonorrhea and sj^philis are univer- 
sally believed to be transmitted exclusively by contact, and 
almost invariably by a special kind of contact. This idea is 
so firmly fixed in the minds of medical men and the laity, 
that no matter how many cases occur which it is impossible 
to trace to their source, no one ever suggests that these 
diseases are air-borne, or that their germs maintain a sapro- 
phytic life. No matter how much the patient may protest, 
it will still be held that the infection is due to contact, and 
in the vast majority of cases to contact involved in the sexual 
act. Gonorrhea, particularly, is believed to be almost never 
transmitted except by the most direct contact; yet there is 
at times as much reason for assuming that the gonococcus 
is air-borne, or clings to the walls of rooms and thence infects 
their occupants, as there is to assume the same for scarlet 
fever. Yet so firmly are we held by tradition that if any of 
us should suggest such an origin for gonorrhea it would pro- 
voke only a smile, while such sources of scarlet fever are 
accepted as well established. 

122 



IXFECTIOX BY COXTACT 123 

Gonorrhea in Babies' Hospital. — The spread of gonococ- 
cus infection in institutions for children is very suggestive of 
the ways in which other infections are transmitted. 

A very interesting account of institutional infection is given 
by Holt. 1 At the Babies' Hospital in New York, from 1894 
to 1898 inclusive, 64 cases of gonococcus vaginitis were admit- 
ted, and 16 cases developed in the hospital. In the summer 
of 1899, three children suffering from gonococcus vaginitis 
were inadvertently admitted to the country branch of the 
hospital, and though the danger was realized, and every effort 
was made to prevent the extension of the disease, by pro- 
viding separate nurses for the infected cases, by washing the 
napkins separately, and boiling and disinfecting them, never- 
theless 15 girls contracted vaginitis. In 1901 similar trouble 
was experienced, and notwithstanding the most vigorous 
measures of isolation and napkin disinfection, 22 cases devel- 
oped in the one cottage to which the three original cases 
were admitted. The physicians were inclined to look upon 
general house infection as the only explanation of the origin 
of the cases. In November, 1902, a new hospital building 
was occupied for the first time, and it was hoped that it could 
be kept free from the disease, but 5 cases were unwittingly 
admitted during the first six months, and 29 cases of vagi- 
nitis and 8 of gonococcus arthritis developed in the institu- 
tion. During the year, 13 cases were admitted, and 66 were 
contracted in the hospital. Although the infected cases were 
all strictly isolated, on two occasions a child, even in another 
part of the hospital, developed the disease. For a time 
napkins were discarded and pads used, which could be 
burned; separate thermometers, baths and supplies were 
required for each child; wash cloths were burned, and tub 
baths forbidden. Bed clothing was disinfected with the 
greatest care. There was thought to be absolutely no 
opportunity for direct contact between child and child. 
When diphtheria or scarlet fever persists in an institution in 
1 Holt, N. York M. J. [etc.], 1905, LXXXI, 521. 



124 THE SOURCES AND MODES OF INFECTION 

such a manner, it is at once attributed to persistent infection 
of the building itself, and it is suggested by Holt as a pos- 
sibility in this instance also. 

Carried by Nurses. — But the gonococcus is an excep- 
tionally frail organism, and it is impossible to believe that 
persistent infection of a building or its contents can occur. 
Actually, in the Babies' Hospital, it was found that the nurse 
was the carrier of the germs from child to child, and the two 
cases which developed in distant wards, and which were sup- 
posed to be perfectly isolated and under the care of different 
nurses, were attended by the same night nurse who looked 
after the infected cases. Finally, when the strictest disin- 
fection had failed to check the disease, it was at last con- 
trolled by requiring that the nurses should practice a strict 
medical asepsis, and disinfect the hands in every instance 
immediately after bathing or changing the napkins of each 
child. Here was a disease which continued to spread after 
the erratic and persistent manner of scarlet fever and diph- 
theria, and which was shown to depend exclusively upon con- 
tact infection. Air-borne infection and fomites infection can 
have no part in institutional gonococcus infections, for the 
gonococcus dies so quickly that such modes of transfer- 
ence are impossible. Yet this infection is most persistent 
and troublesome in many institutions for the care of young 
children. 

Contact not always Direct. — Gonorrheal infection is not 
only quite common in institutions, but it is often found in 
infants and young children in their homes. It is believed 
to result usually from the child sleeping with its parents, or 
to direct contact with the hands of the mother while washing 
or dressing the child. I have also known of cases of the direct 
transfer of the disease on instruments in a physician's office. 

It has thus been necessary to modify our conception of 
the mode of transmission of gonorrhea, and although it is 
still conceived of as due exclusively to contact infection, it 
is now recognized that the contact need not always be direct 



INFECTION BY CONTACT 125 

between the sick and the well, but some infected person or 
thing may act as intermediary. Yet from what is known of 
the weak resistance of the gonococcus, the interval of time 
must be brief. The term contact infection as now employed 
means just that kind of transference of rather fresh infecting 
material from one to another. It does not necessarily imply 
actual contact between sick and well, but it does imply that 
there are no long intervals of time in which the infective 
materials may become dry and inert. The transfer of gonor- 
rheal pus from child to child on a syringe, or on the fingers 
of the nurse, are examples of contact infection. If the pillow 
used by an infected child were put away for a week or two, 
and when brought out caused ophthalmia in the infant who 
used it, it would be an example of fomites infection. The 
distinction between the two types of disease transference, 
though not sharply or accurately defined, is a reasonable and 
practical one. Thus every one admits that gonorrhea is fre- 
quently transferred by indirect contact infection, as it may 
be called, but it is never suggested that this disease is spread 
by fomites. 

Syphilis spread solely by Contact. — While it appears to 
be pretty well determined that Treponema pallida is the 
cause of syphilis, we have as yet no data as to the cultivation 
of this organism or its persistence outside of the body. Its 
cultivation outside the body certainly is not easy, and it may 
be suspected that its life is short; but it is not impossible 
that the virus may retain its virulence for some days or weeks, 
as does that of rabies, variola and vaccinia. At present we 
have to rely solely on clinical evidence as to these points, and 
the universal opinion of this much studied disease is that 
the virus develops only in human beings (and some of the 
apes), that it is not very persistent, and that it is trans- 
mitted solely by contact. No one has ever suggested that 
syphilis is an air-borne disease in the ordinary sense, though 
one or two cases of droplet infection have been reported. 1 
1 Buckley, Syphilis in the Innocent, N. Y., 1894, 176. 



126 THE SOURCES AND MODES OF INFECTION 

No matter how obscure may be the origin of cases, no one 
would attribute them to aerial infection, or to dwelling in an 
infected house. Infection during the sexual act is undoubt- 
edly the cause of by far the larger proportion of the cases of 
this disease, yet in the aggregate a great number of cases are 
caused in other ways. 

Non-sexual Contact. — Buckley in the work just quoted 
shows that probably ten per cent of the initial lesions are 
extragenital. Exceedingly infectious lesions are at a certain 
stage of this disease frequently found in the mouth, so that 
it is not surprising that the second most important source 
of the disease is another form of direct contact, namely kiss- 
ing. Other forms of. direct contact are often reported, as 
nursing, and sucking wounds. That mediate contact by 
means of all sorts of articles infected with saliva, or more rarely 
other secretions, is common, is now well known, and Buck- 
ley has collected many hundreds of instances of such modes 
of transference. Among various bearers of infection reported 
by Buckley may be mentioned cups, glasses, spoons and other 
eating-utensils, pipes, toilet articles, underclothing, bathing 
suits, handkerchiefs, bedding, pins, string, wind instruments 
of all kinds, glass blowers' tubes, pencils, coins, nursing-bottles, 
sponges, syringes, surgeons' instruments, dentists' tools and 
barbers' utensils. But the possible ways in which the disease 
can be spread by indirect contact are almost infinite, and the 
larger part of Buckley's book is occupied by their enumeration. 
A perusal of these reports is extremely interesting, for while it 
is not claimed that every case narrated was caused in the man- 
ner assumed, yet it is evident that all such modes of trans- 
mission are possible, and one is greatly impressed by the vast 
number of ways in which fresh secretions maybe passed from 
one to another. While the time during which the various 
articles retained their infection is unknown, or at least is not 
given in the reports of cases, it is apparent that almost none 
of the instances of mediate contact were the result of long per- 
sistent infection. Fomites infection is not an important 



INFECTION BY CONTACT 127 

factor in the spread of syphilis. Buckley 1 says that the 
danger from soiled clothing, rags, or second-hand garments 
" is infinitely less than is commonly supposed, and relatively 
few instances have been recorded, and none of these are very 
clear or satisfactory." In the few instances which he gives, 
the infective material might well have been very fresh. 

Typhoid Fever by Contact. — Of late years a great deal 
has been written about the transmission of typhoid fever by 
contact from case to case, and this mode of infection appears 
to have attained greater prominence in connection with this 
than with any other of the common infectious diseases. My 
attention was first drawn to the importance of contact infec- 
tion in typhoid fever by the vivid description given by Sedg- 
wick of an outbreak which he investigated in 1892 in 
Bondville, Massachusetts. He says: 2 " Children abound; and, 
as there are no fences, and because it is the custom, they mingle 
freely, playing together and passing from house to house. 
The families are of that grade in which food always stands 
upon the table ; meals are irregular except for those who must 
obey the factory bell. The children play awhile, then visit 
the privies, and with unwashed hands finger the food upon 
the table. Then they eat awhile and return to play. Or, 
changing the order of things, they play in the dirt and eat 
and run to the privy, then eat, play, and eat again, and this 
in various houses and in various privies. For them, so long 
as they are friendly, all things are common, — dirt, dinners 
and privies; and, to illustrate exactly how secondary infection 
may go on, I may describe in detail one case which I personally 
witnessed. A whole family (of six or more) was in one room. 
Four of them had the ' fever.' Two of these were children 
in the prodromal stage. A table stood by the window covered 
with food, prominent among which was a big piece of cake. 
It was early September, and a very warm day; but every 
window was shut and the odor sickening. Flies innumerable 

1 Buckley, Syphilis in the Innocent, New York, 1894, 156. 

2 Sedgwick, Rep. Bd. Health Mass., Bost., 1892, 736. 



128 THE SOURCES AND MODES OF INFECTION 

buzzed about, resting, now on the sick people, now on the 
food. A kind-hearted neighbor was tending the baby. By 
and by one of the children having the fever withdrew to the 
privy, probably suffering with diarrhea, but soon returning, 
slouched over to the food, drove away some of the flies, and 
fingered the cake listlessly, finally breaking off a piece, but 
not eating it. Stirred by this example, another child slid 
from his seat in a half-stupid way, moved to the table, and, 
taking the same cake in both hands, bit off a piece and swal- 
lowed it. The first boy had not washed his hands, and if 
the second boy suffered from secondary infection, I could not 
wonder at it. 

"This was one case; but I have seen so often the table of 
food standing hours long in the kitchen, and serving as one 
station in the dirty round of lives like these, that it is easy 
for me to understand how dirt, diarrhea and dinner too often 
get sadly confused. The privies had been obviously in bad 
condition, and, from some, filthy streams ran down between 
them and the houses. In and around these streams the chil- 
dren played. Given any original imported case, the infection 
might easily have reached these trickling streams. Children's 
fingers might thence carry the germs to the food, and thus 
the journey of the germs from one living intestine to another 
be completed. Or, again, given in such a community an 
imported case and no disinfection, as was the condition here 
at first. The importer, while in the early stages, handles with 
unclean hands food for others; or the clothing of such a per- 
son gets infected and is handled; there need be, then, no diffi- 
culty in completing the history. It follows as a matter of 
course." 

Contact Typhoid in Spanish War. — Probably the report 
of Reed, Vaughan and Shakespeare 1 did more than anything 
else to call attention to the importance of contact infection 
in the epidemiology of this disease. This commission found 

1 Abst. of Rep. on the Origin and Spread of Typhoid Fever in U. S. 
Military Camps during the Spanish War of 1898, Wash., 1900. 



INFECTION BY CONTACT 129 

that infected water played little part in the development of 
typhoid fever in the camps. They also found that probably 
every regiment brought into camp one or more mild unrec- 
ognized cases or carriers, and that these were the starting 
points of outbreaks. It was shown that the fever was not 
evenly distributed through the regiments, but was more or 
less localized in companies or squads (p. Ill et seq.). 

While they attributed a certain amount of the disease to 
carriage by flies and by dust, they considered contact infec- 
tion from man to man the most important cause. Of 1608 
cases especially studied, and which were accurately located 
as to place and time, 35.01 per cent were directly connectible 
and 27.79 per cent indirectly connectible attacks; total con- 
nectible attacks, 62.80 per cent (p. 184). Owing to the unsat- 
isfactory methods, or lack of method, of excreta disposal, the 
shoes, clothing and hands of the men, as also the blankets 
and tentage, became more or less soiled with excreta, and 
infection of the men became easy, and in fact unavoidable. 
Men detailed as hospital orderlies were, after they had per- 
formed the duty of emptying bedpans, seen to go directly 
to their meals without washing their hands, and even to dis- 
tribute food to their comrades. 

In South Africa. — Similar conclusions were arrived at by 
the surgeons who studied typhoid fever, which proved equally 
disastrous to the English, in the Boer War, but on the 
whole, however, the English, while recognizing the impor- 
tance of contact infection, did not place so much stress 
upon it as did the Americans. 1 

Contact Typhoid in Civil Life. — Outbreaks in civil life 
have of late frequently been attributed largely to contact 
infection. Winslow 2 reported an outbreak in Newport, R. I., 
which probably had its origin in an infected well, but which 

1 Col. Lane-Notter, Tr. Epidemiol. Soc, Lond., 1904, XXIII, 149; 
J. Roy. Army Med. Corps, Lond., 1905, IV, 587, 693; Tooth, Brit. M. 
J., Lond., 1901, I, 642. 

2 Winslow, Technology Quarterly, 1901, XIV. 



130 THE SOURCES AND MODES OF INFECTION 

was continued by contact infection. He coined the word 
" prosedemic " to describe this extension of the disease from 
case to case. Water-borne and milk-borne outbreaks of 
typhoid fever usually develop suddenly, a large number of 
cases being reported within a short time. That they do not 
end so suddenly but, even after the infected water and milk 
are eliminated, continue, decreasing gradually, is a phenome- 
non which becomes apparent from the examination of the 
charts of such outbreaks. This prolongation of the outbreak 
is due to the prosedemic infection of Winslow, and has been 
noted by Whipple 1 for water outbreaks, and by Trask 2 for 
milk outbreaks. During a water-borne outbreak at Lincoln, 
England, from 50 to 60 per cent of the cases were due to 
personal contact. 3 

Municipal Outbreaks. — Many local outbreaks have been 
believed to be due almost, if not quite, exclusively to contact 
infection. Such an outbreak was reported by Weston and 
Tarbett in Knoxville, 4 Jordan in Winnipeg, 5 Magrath in 
Springfield, 6 Noetel in Beuthen, 7 and Weil in Rathsweiler. 8 
Freeman 9 states that the majority of the outbreaks in the 
smaller towns of Virginia appear to be due to contact infec- 
tion. The authority of Koch has done much to direct atten- 
tion to the importance of contact infection in the spread of 
typhoid fever in civil life. In a report on a village outbreak 
in Trier 10 he says that small country epidemics will usually 

1 Whipple, Typhoid Fever, 1908, 209. 

2 Trask, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. 
No. 41, 38. 

3 Pub. Health, Lond., 1905, XVIII, 129. 

4 Weston and Tarbett, Am. Pub. Health Ass. Rep., 1907, XXXIII, 
Pt. 1, 63. 

5 Jordan, Abst. in J. Am. M. Ass., Chicago, 1905, XLIV, 563. 

6 Magrath, Am. J. Pub. Hyg., Bost., 1905, I, 467. 

7 Noetel, Ztschr.f. Hyg.u.Infectionskrankh.,Leipz., 1904, XLVII, 211. 

8 Weil, Med. News, N. Y., 1904, LXXXIV, 467. 

9 Freeman, J. Am. M. Ass., Chicago, 1909, LIII, 1263. 

10 Koch, Die Bekampfung des Typhus, Berlin, 1903. 



IXFECTIOX BY COXTACT 131 

be found to be due to this mode of infection. In the particu- 
lar outbreak investigated all the cases were found to be due 
to contact, that is, to the direct transfer from person to per- 
son, and the source was in most instances unrecognized mild 
cases, often in children. He then describes conditions very 
much like those reported by Sedgwick. Fecal matter was 
observed in the dooryards where it could readily infect the 
children playing about, and would certainly be carried indoors 
on their shoes. 

Fulton, 1 Egbert 2 and others have shown that typhoid fever 
prevails far more extensively in the country than in the city. 
Formerly, when less was known about the etiology of the 
disease, polluted well water was believed to be the chief factor 
in its causation, but it now appears that it is far more likely 
to depend on contact infection. 

In Hospitals. — Typhoid fever frequently develops in hos- 
pitals and other institutions, presumably by contact infec- 
tion. Occasionally explosive outbreaks due to infected milk 
or food are observed, but many institutional outbreaks are 
characterized by a slow and irregular development of cases. 
The disease chiefly attacks those who are brought in close 
contact with the sick, physicians and especially nurses. Fifty 
or sixty years ago few cases of hospital infection were re- 
corded. It is suggested that this may have been due to the 
fact that nurses in those days were usually women well along 
in years, and therefore not so susceptible to the disease, and 
usually, perhaps owing to the greater prevalence of the dis- 
ease, immune. During recent years typhoid fever among 
nurses and ward tenders has been quite common. Joslin 
and Overlander 3 state that 26 of 322 nurses at the Mas- 
sachusetts General Hospital, and 12 of 94 ward tenders, con- 
tracted typhoid fever while on duty. It is said that in the 
London hospitals typhoid fever is twenty times as common 

1 Fulton, J. Am. M. Ass., Chicago, 1904, XLII, 73. 

2 Egbert, Am. Med., Phila., 1905, IX, 649. 

3 Joslin and Overlander, Boston M. & S. J., 1907, CLVII, 428. 



132 THE SOURCES AND MODES OF INFECTION 

among nurses as among women of the same ages in other 
occupations. 1 Goodall 2 says that during the years 1892- 
1899 there were treated in the London hospitals 5913 typhoid 
patients, and 100 attendants contracted the disease. In four 
hospitals not admitting typhoid fever no cases developed. 
Schuder, 3 Neufeld/ McCrae, 5 Talayrach, 6 Edsall 7 and others 
have reported an excessive prevalence of typhoid fever among 
the attendants on cases of this disease in hospitals, and they 
have also noticed numerous instances in which it has devel- 
oped among other patients. Nurses and others infect their 
hands while caring for typhoid patients, and then without 
washing the hands, or after careless washing, infect their 
own mouths directly, or by handling their food and drink. 
Through the same carelessness they also infect other patients. 
Neufeld refers to the transfer of the germs on a thermometer 
and in a bath. Edsall has seen a nurse given the double 
duty of emptying the bedpans of typhoid cases and pre- 
paring special diet, and a patient was observed to empty a 
bedpan and then proceed to his dinner without washing his 
hands. Nurses also wipe out the mouths of patients with a 
bit of gauze on the finger, a procedure which was believed by 
Holt to be one of the means of spreading gonorrheal infec- 
tion in the Babies' Hospital. By introducing strict cleanli- 
ness Edsall was able to stop this transference of the disease. 
In Other Institutions. — Sometimes quite marked out- 
breaks occur in institutions, due presumably to contact in- 
fection. Usually water, milk and other food as sources of 
infection can be excluded, and the irregular and slow devel- 
opment of the cases, and perhaps the discovery of carriers or 

1 Pub. Health, Lond., 1905, XVIII, 142. 

8 Goodall, Trans. Epidem. Soc, Lond., 1900. 

3 Schuder, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., XXXVIII, 251. 

4 Neufeld, Kolle u. Wassermann, Handbuch [etc.], Jena, 1903, II, 296. 

6 McCrae, Mod. Med. [Osier], Phila. & N. Y., 1907, II, 82. 

• Talayrach, Arch. d. med. et de pharm. milit., Par., 1903, XLII, 393. 

7 Edsall, Am. J. M. Sc, Phila., 1908, n. s., CXXXV, 469. 



INFECTIOX BY COXTACT 133 

missed cases, renders the extension of the disease by per- 
sonal contact highl} T probable. In an almshouse in New 
Haven, 1 37 cases occurred during a period of some months. 
Mild cases were concealed and worked in the kitchen, and 
it was impossible to teach the inmates cleanly habits. At a 
soldiers' home at Lafayette, Indiana, there were 65 cases 
due to contact infection, probably chiefly from the physician. 2 
At the State Hospital for the Insane at Trenton there 
occurred between April 8 and August 13, 1907, 80 cases 
with 16 deaths, due in all probability to contact infection, 
largely in the kitchen and pantry. 3 Ravenel 4 reports an 
outbreak in a boarding house at the University of Wisconsin, 
where 41 cases developed, probably as the result of a patient 
working in the pantry during the prodromal period of his 
illness. Sedgwick 5 reports the case of a chambermaid, and 
also of a laundress, who contracted typhoid fever from 
handling soiled linen. A waitress, also, who ate bread cut 
by the other two, developed the disease. Wolcott tells of 
the matron of a hospital who caught the disease from han- 
dling infected bedding and neglecting to wash the hands. 
McCrae 6 reports an instance of infection from careless han- 
dling of typhoid cultures in the laboratory, and a similar 
case occurred in an insane asylum at Northampton, Mass. 7 
Dr. Mann tells me that a number of nurses eating at the 
same table in the Homeopathic Hospital in Boston con- 
tracted typhoid fever, probably from a waitress whose sister 
was sick with the disease, and who herself was perhaps a 
carrier. 

1 Rep. Bd. Health, New Haven, 1905, 6. 

2 Hurty, J. Am. M. Ass., Chicago, 1909, LIII, 1263. 
■ Rep. St. Bd. Health, New Jersey, 1907, 149. 

4 Ravenel and Smith, K. W., J. Am. M. Ass., Chicago, 1909, LII, 
1635. 

5 Sedgwick, J. Mass. Ass. Bds. Health, Bost., 1900, X, 148. 
8 McCrae, Mod. Med. [Osier], Phila. & N. Y., 1907, II, 82. 
7 Rep. Bd. Health, Mass., Bost., 1899, 762. 



134 THE SOURCES AND MODES OF INFECTION 

Contact on Shipboard. — Many of the instances of infec- 
tion by carriers referred to in Chapter II were almost cer- 
tainly the result of contact infection, and many more could 
be easily collected. Occasionally small outbreaks occur on 
shipboard, where it is possible to exclude all modes of infec- 
tion but contact. Thus, 9 cases on an Atlantic liner were 
traced to a saloon steward. 1 On the United States ship Con- 
necticut there were three outbreaks in 1907, almost certainly 
due to contact infection. 2 

In the Family. — During 1908 I noted three small out- 
breaks of typhoid fever in Providence, due apparently to con- 
tact infection. In one instance there were 10 cases in three 
closely related families, in another 8 cases in three such 
families, and in the third outbreak there were 7 cases in 
two families. Such family outbreaks are noticed in Provi- 
dence nearly every year, and they are referred to so often 
in current medical literature that it does not seem necessary 
to give additional references. Contact outbreaks in hotels 
and boarding houses, as well as in various public institutions, 
are also frequently reported. Hill in Birmingham, in 1898, 
traced 10 per cent of the typhoid-fever cases to contact with 
other cases. In Manchester in the same year about 13 per 
cent were traced in the same way, and in 1906, 36.8 per cent. 
Edsall attributed 27 per cent of 250 cases to contact, and 
Forster 117 of 386 cases, and McCrae 68 of 500 cases. It 
would be easy to prolong the discussion and show that med- 
ical men are everywhere attributing more and more impor- 
tance to contact infection in this disease. It is to be noted 
that in few of the reported instances of contact infection is 
there any direct and conclusive proof that the disease was 
caused in the manner alleged. The evidence is by no means 
so convincing as to mode of infection as it is in so many 
water-borne and milk-borne outbreaks, and from the nature 
of things it rarely can be so. 

1 Rep. Med. Off. Health, Glasgow, 1907, 147. 

2 McDonnold, Mil. Surgeon, Carlisle, Pa., 1908, XXIII, 29. 



INFECTION BY CONTACT 135 

Evidence of Contact Infection. — But when water and food 
as vehicles of infection are excluded, when the disease devel- 
ops in persons who are in contact with the sick or with car- 
riers, and when the fingers, possibly or perhaps evidently 
soiled with excreta, are seen to touch food, eating-utensils, 
and sometimes the lips, the probability of the development 
of the disease in this manner is so evident that observers 
are constantly seeing in contact infection the cause of family, 
institutional and community outbreaks of this disease. The 
importance now attributed to contact infection is the result 
of a careful estimate of probabilities. 

Amount of Contact Infection. — In 1908 there were 11,375 
deaths from typhoid fever in the registration area of the 
United States, which doubtless means considerably over 
100,000 cases. The registration area includes about one-half 
the population of the country. While a certain amount of 
typhoid fever is caused by milk, it must be a very small 
fraction of the great total. As will be shown, milk outbreaks 
are usually well marked, and probably not a very great deal 
of milk-borne infection escapes notice. Again, while in some 
cities the larger part of the typhoid fever is due to infected 
water, it is not so in most cities, and certainly only a small 
part of the total typhoid fever in the country can be traced 
to such a source. It is not likely in my own city for instance 
that more than 20 per cent of the 4300 cases of typhoid fever 
during the past twenty-five years have been due to infected 
water or milk; and infected oysters, celery, etc., certainly 
play a very unimportant part in the causation of the disease. 
As we shall see, it is improbable that air-borne infection 
or dust infection is of any moment in civil life. The only 
other important source of typhoid fever which has been sug- 
gested is fly-borne infection. It will be shown also that 
infection by means of flies probably accounts for only a 
small part of our typhoid fever. By exclusion, then, we 
are led to the conclusion that contact infection is the chief 
source of our typhoid fever. 



136 THE SOURCES AND MODES OF INFECTION 

Why should we not, in the absence of direct evidence as 
to other modes of infection, assume at once that contact, 
that is, the more or less direct transfer of infective material 
from person to person, is the principal source of contagious 
disease ? Why neglect the most obvious and direct mode 
of transfer in favor of more circuitous paths ? There are 
several reasons why contact infection in this disease has been 
neglected. 

Why Contact Infection has been Neglected. — One reason 
has been the undue emphasis laid upon other modes of trans- 
mission. Formerly air infection was considered of great 
moment, and as this fell into disrepute, undue weight was 
attached to water and milk infection, partly, no doubt, because 
of the dramatic character of so many outbreaks. Another 
reason for doubting the importance of contact infection is 
the prevalent notion that typhoid fever is essentially an intes- 
tinal disease, and that it must be caused by infected food. 
It now appears that typhoid fever is not an intestinal disease, 
and in some cases the intestines are not involved and the 
feces are free from bacilli during the whole sickness. But 
the bacilli are found in the blood stream in the earliest stages, 
and it seems to be more likely that they enter the circulation 
through the upper part of the alimentary tract than through 
the intestines after running the gauntlet of the gastric secre- 
tions. Even if it be denied that the tonsils and stomach are 
the portals of entry of the typhoid bacilli, it is highly probable 
that bacilli taken into the mouth in small masses find their 
way to the lower part of the alimentary tract by means of 
the small quantities of saliva which are constantly swallowed. 
It has certainly been demonstrated that tubercle bacilli are 
swallowed and thus reach the intestines. 

People are not Cleanly. — Then, too, contact infection 
in typhoid fever supposes an intimacy with the most offen- 
sive substances, which most persons would vehemently deny. 
Nevertheless it appears that the fingers of human beings, 
and secondarily everything that the fingers touch, are fre- 



INFECTION BY CONTACT 137 

quently contaminated with excremental matter. The colon 
bacillus is for all practical purposes a good test for the pres- 
ence of excrement, and it is somewhat of a shock to learn that 
it is found on the hands of five to ten per cent of ordinarily 
cleanly people. Winslow x and Hall, 2 while studying the dis- 
semination of typhoid fever by carriers, recovered fecal 
bacteria from the finger nails and hands after the usual pro- 
cedures following the use of the closet and toilet. An inspec- 
tion of the privies or water-closets in railway stations, 
factories, shops and tenement houses shows that they usually 
present evidence of contamination with feces and urine, and 
in many instances are constantly in a horribly filthy condition. 
It is only in the better class of hotels and residences that these 
apartments are kept in even an apparently cleanly condition, 
and this is only by dint of constant vigilance and frequent 
cleansing. There can be no doubt that even very careful 
people frequently infect the seat, their fingers, the pull, the 
door, etc., and that in a large proportion of privies and water- 
closets the users almost certainly infect their fingers with at 
least traces of their own or others' excremental matter. Yet 
how many persons are there who invariably wash the hands 
after the use of a closet ? How many make it a rule never 
to put the fingers in the mouth ? Yesterday I saw a workman 
carrying a can of beer to his friends. His thumb was im- 
mersed a couple of inches in the beverage. Had he washed 
his hands after leaving the barroom water-closet ? At a 
recent sanitary convention I noticed the colored waiter stick 
his finger into a glass which he, however, did not remove, and 
which the speaker soon drank from. What was the recent 
history of that finger ? Does the fruit peddler wash his hands 
after using the tenement privy before he ventures to sort his 
fruit ? Do the waitress, the milk peddler, the candy seller, 
the Pullman porter, the soda-water clerk, the baker's boy, 
the delicatessen man always wash the hands before taking 

1 Winslow, J. Mass. Ass. Bds. Health, Bost., 1903, XIII, 144. 

2 Hall, Rep. Med. Off. Health, Bristol, Eng.. 1908, 27. 



138 THE SOURCES AND MODES OF INFECTION 

up their work? Are the toilets in their places of business 
so cleanly that such a precaution is not necessary ? How- 
ever shocking it may seem, it is certain that it requires only 
a little observation to demonstrate that the path from intes- 
tines to mouth is not always a circuitous one. 

Contact with Carriers. — Until recently it would have 
been argued that contact infection is not an important factor 
in typhoid fever because only a small proportion of the cases 
can be shown to have been in contact with this disease, and 
because the large proportion of cases of this fever are more 
or less isolated in their homes because of the sickness. But 
we now know that there are vast numbers of mild unrecog- 
nized cases, and most important of all, that the number of 
carriers is very great. There are doubtless 200,000 cases of 
this disease in the United States each year. If only 3 per 
cent of these become chronic carriers, and if a carrier remains 
such only three years, we should have a carrier population 
of 18,000 persons, practically all unknown and taking no pre- 
cautions against infecting others. If we add to these the 
25 per cent of convalescents, who for some weeks are excret- 
ing the bacilli in their urine, it appears that there is a very 
respectable army of unrecognized sources of typhoid infection. 

At present we have no definite knowledge of the origin of 
the larger number of our cases of typhoid fever. In view 
of the almost universal careless habits of the people, and 
the great number of carriers, why not adopt as a working 
hypothesis the most obvious source of infection, infection by 
contact ? 

Danger from Privies. — This view that contact infection 
is the most important factor in the causation of this disease, 
is borne out by the observation that the more promptly and 
effectively human excrement is disposed of, the less chance 
there is for contact infection and the less the disease prevails. 
When the disposal is exceptionally bad, as in army camps, 
lumber, mining and railroad camps, then this disease is al- 
most always very common. In thoroughly sewered and clean 



INFECTION BY CONTACT 139 

cities, provided the water and milk are not contaminated, 
typhoid fever is comparatively rare. The privy vault stores 
up fecal matter on the premises and is rarely kept as clean 
as a water-closet, and the area around privies is often filthy 
also. It has often been noted that the removal of privy 
vaults has been followed by a decrease in typhoid fever. In 
Providence the disease fell off forty per cent after most of the 
privy vaults were abolished. Many other American cities in 
which typhoid fever is not maintained by a polluted water 
supply, show a steadily decreasing prevalence of this disease 
as privy vaults are gotten rid of. In England Pringle 1 has 
shown that in fourteen towns with middens the typhoid rate 
was 0.25 per 1000, while in fourteen water-closet towns it 
was 0.19. In Ipswich there was a marked decrease in typhoid 
fever following the removal of the middens. 2 A similar de- 
crease was noted in Oldham, Leicester 3 and other cities. On 
the other hand more " pail closets " remain in Nottingham 
than in most English cities, and to this Boobbyer 4 attributes 
the fact that typhoid fever has decreased less in that town 
than in the other great towns of England. Like reports of 
a decrease in the disease following removal of privies come 
from such widely separated places as Winnipeg 5 and Mel- 
bourne. 6 

There are also numerous reports to the effect that in the 
same town typhoid fever is much more common in houses 
without water-closets than in those with them. This may 
be due in part to the storing of fecal matter on the premises 
of the former, and it may be due also to the fact that houses 
with privies are usually of a poorer class, and the inhabitants 
less cleanly in their personal habits, or to other reasons; but 

1 Pringle, Pub. Health, Lond., 1902-03, XV, 630. 

2 Pub. Health, Lond., 1908-09, XXII, 414. 

3 Rep. Med. Off. Health, Leicester, Eng., 1908, 29. 

4 Boobbyer, Rep. Health of Nottingham, 1908, 53. 
6 Rep. Dept. Pub. Health, Winnipeg, 1908, 4. 

6 Jamieson, J., Australas. M. Gaz., Sydney, 1903, XXII, 56. 



140 THE SOURCES AND MODES OF INFECTION 

these facts of typhoid distribution accord with the view that 
the disease is largely spread by contact from person to 
person. In Birmingham, 1 the incidence of typhoid fever in 
" pail " and water-closet houses was as 65 to 43, and there 
has been a steady decrease in the disease as the " pail 
closets" have been abolished. In Nottingham there was (in 
ten years) 1 case in each 37 houses with privies, and 1 in 
each 558 water-closet houses; in Salford it was 1 to 20 and 
1 to 42 respectively, 2 and in Gorton the cases were two 
or three times as numerous in privy houses as in water- 
closet houses. 3 At Leigh, 4 typhoid fever was four times 
as prevalent among colliery workers as among the rest of the 
population, owing, in the opinion of the inspector, to the filthy 
mode of excreta disposal in the mines. In Glasgow 5 second- 
ary cases of the disease developed in 23 per cent of the cases 
in houses with privies and in 6 per cent of the cases in houses 
with water-closets. 

Every one who has had practical experience in sanitary 
inspection work knows that privy vaults not only serve as 
storehouses for excrement, but their presence encourages its 
careless disposal in the yards and on ash heaps. The filthy 
condition of the ground about the houses, leading to contami- 
nation of feet and hands of children, as reported by Sedgwick 
and by Koch, is rarely noticed on premises provided with 
water-closets. It may be urged that the excess of typhoid 
fever in privy towns is due to infection by flies rather than 
infection by contact, and this may be true to some extent; 
but if flies were the chief factor we should scarcely expect 
a great difference between water-closet and privy houses in 
the same town. So also the infection of miners, as noticed 

1 Rep. Health of Birmingham, 1906, 49, and 1908, 49. 

2 Pringle, Pub. Health, Lond., 1902-03, XV, 630. 

8 Martin, Pub. Health, Lond., 1904-05, XVII, 709. 
4 Sweeting, Rep. Med. Off. Local Gov. Bd., Lond., 1907-08, XXXVII, 
57. 

6 Rep. Med. Off. Health, Glasgow, 1902, 97. 



IXFECTIOX BY COXTACT 141 

by Sweeting, cannot be due to flies. In Providence after the 
removal of privies the decrease in typhoid fever was as great 
in winter, when there were no flies, as during the fly season. 

Amebic Dysentery. — There is no reason why amebic 
dysentery may not be transmitted by personal contact, but 
if, as is generally believed, the ameba is quite widely dis- 
tributed in the soil, it is likely that in countries where the 
disease is endemic, man is the least common source of infec- 
tion. Nevertheless cases do develop from contact with other 
cases. Lemoine 1 has reported such infections in France, in 
one instance at least, probably due to the use of the same 
bedpan, douche, etc. The infecting case was a carrier of 
ten years' standing. Allan 2 writes that in Charlotte, N. C, 
he observed four cases of amebic dysentery which he believed 
were due to contact with chronic carriers. 

Bacillary Dysentery. — Bacillary dysentery, like typhoid 
fever, is a great scourge of military life, and outbreaks of a 
serious character are not rare in institutions such as hospitals 
for the insane. The bacillus is found in the feces of the 
patients and also in convalescents. There is every reason 
for believing that this disease, like typhoid fever, is frequently 
spread by more or less direct contact. 3 Conradi 4 described 
a village outbreak near Metz where 70 cases occurred during 
a period of three months. Several carriers were found in 
infected families, and conditions favoring contact infection 
were noted, very similar to those observed in the outbreaks 
of typhoid fever studied by Koch in Trier. Dodge 5 reports 
the case of a laboratory worker who got some of a culture 
of the dysentery bacillus in his eye; the tears ran profusely 
and were swallowed, and in twenty-four hours an attack of 

1 Lemoine, Bull, et mem. Soc. med. de hop. de Par., 1908, 3 s., XXV, 
640. 

2 Allan, Med. Rec, N. Y., 1910, LXXVII, 63. 

3 Shiga, Mod. Med. [Osier], Phila. & N. Y., 1907, II, 781; Scheube, 
Diseases of Warm Climates, 2d Ed., Phila., 466. 

4 Festschrift von Robert Koch, 1903, 555. 

5 Dodge, Am. Pub. Health Ass. Rep., 1905, XXX, 310. 



142 THE SOURCES AND MODES OF INFECTION 

dysentery developed. An outbreak of 49 cases, developing in 
the characteristic slow irregular manner of contact outbreaks, 
was reported in the Connecticut Hospital for the Insane. 1 
Kruse 2 reports a similar outbreak in Germany, and two in 
Holland. Epidemic dysentery is quite common in hospitals 
for the insane, and its prevalence is explained as due chiefly 
to contact infection, for the carelessness of many patients 
and the impossibility of controlling their habits offer every 
opportunity for this sort of diffusion. 3 

Cholera and Contact. — If typhoid fever and dysentery 
are spread by means of contact infection, we should expect 
that cholera would be. That less is written about it is due 
probably to the fact that in recent years less attention has 
been paid to cholera than to the more common diseases. 
The literature relating to typhoid fever has of late been many 
times more voluminous than that relating to cholera. Never- 
theless most writers attribute some importance to contact 
infection in this disease, and some consider it an etiological 
factor of very great importance. The filthy conditions of vil- 
lage life described by Sedgwick in America and Koch in Ger- 
many as giving rise to typhoid fever, are far surpassed in 
danger by the habits of vast numbers of the poorer people 
who dwell in cholera-infested countries. The opportunities 
for the direct transference of fecal matter from person to 
person are far greater in Asiatic countries than they are with 
us, and a number of writers have emphasized the part played 
by personal contagion in this disease. Gotschlich 4 refers to 

; 1 Rep. St. Bd. Health, Connect., 1903, 234. 

2 Kruse, Deutsche med. Wchnschr., 1901, XXVII, 370, 386. 

3 See Reports of Commissioners in Lunacy (Eng.) since 1903; also 
Heuser, Deutsche med. Wchnschr., 1909, XXXV, 1694; Ryder, Boston 
M. & S. J., 1909, CLXI, 681; Haenisch, Ztschr. f. Hyg. u. Infections- 
krankh., Leipz., 1908, LX, 245; Mott, Tr. Epidem. Soc, Lond., 
1901-02, and Arch. Neurol. Path. Lab., Lond. Co. Asyl., Lond., 1903, 
II, 735; Prior, Australas. M. Cong. Tr., Victoria, 1909, III, 383. 

4 Gotschlich, Kolle and Wassermann, Handbuch [etc.], Jena, 1904, 
IV, 108. 



INFECTION BY CONTACT 143 

this factor, and a number of our officers in the Philippines 
have dwelt upon its importance. Woodruff 1 says that while 
infected water played some part in the great epidemic in 
Manila, the filthy habits of the people were the chief cause 
of the extension of the disease. He speaks of an outbreak 
of eighty cases in a provincial town due to food prepared in 
Manila by a caterer who soon died of cholera. Heiser 2 con- 
siders that the handling of foodstuffs and of the leaves in 
which the betel nut is wrapped, by dealers and prospective 
purchasers, is one of the chief ways in which cholera is spread, 
and McLaughlin 3 considers the " carrier" with filthy habits 
the greatest source of danger. He says that contact infection 
of visitors in the houses of the sick is a common means of 
disseminating the disease. Schumburg 4 reported several 
small outbreaks of cholera near Hamburg caused by contact 
infection. Shakespeare 5 reports several instances in which 
cholera was apparently caused by handling soiled linen, some 
of which might perhaps be considered rather as examples of 
fomites infection. Macrae 6 reports the infection of hospital 
nurses with cholera in a manner similar to the infection of 
nurses with typhoid fever. 

Diarrhea. — Newsholme 7 believes that much infantile 
diarrhea is due to direct contact infection in the home, 
rather than to extraneous bacteria in the milk, and he 
suggests that it is brought about by " sucking infective 
matter from dirty fingers, from dummy teats and in other 
ways." Many other English health officers agree with News- 
holme in thinking that contact infection, entirely outside 

1 Woodruff, J. Am. M. Ass., Chicago, 1905, XLV, 1160. 

2 Heiser, J. Am. M. Ass., Chicago., 1907, XLVIII, 856. 

3 McLaughlin, J. Am. M. Ass., Chicago, 1909, LII, 1153. 

4 Schumburg, Ztschr. f. arztl. Fortbild., Jena, 1905, II, 567. 

5 Shakespeare, Rep. on Cholera in Europe and India, U. S. Gov. 
Printing Office, 1890, 81. 

8 Macrae, Indian M. Gaz., 1909, XLIV, 361. 

7 Newsholme, J. Hyg., Cambridge, 1906, VI, 139. 



144 THE SOURCES AND MODES OF INFECTION 

the milk, plays no inconsiderable part in the causation of 
diarrhea. 1 

Hookworms. — Diseases caused by worms are only 
incidentally referred to in this book, but there is one of 
these which is of considerable interest in this connection. 
Hookworm disease, in some respects, bears a considerable 
resemblance to bacterial infections, since constitutional 
symptoms, as marked anemia and debility, are present, due 
presumably to the formation of toxic substances, as well as to 
the direct loss of blood. 2 Moreover, immunity seems to be 
developed, and the worms are often found in persons who 
present no symptoms. Hookworm disease, which had been 
known for many years in Europe, where it had been shown 
to be due to a small worm, Anchylostoma duodenalis, was, 
as a result of scientific work following the Spanish War, 
particularly that of Ashford in Porto Rico, found to be 
very prevalent, not only in the West Indies, but also, as 
shown by Stiles, in our southern states. Stiles, however, 
found that our disease is due to a worm slightly different 
from the European species, and which has been named 
Uncinaria americana. 

The disease, known now as uncinariasis, or anchylostomia- 
sis, is due to the growth of the worms, which are about half 
an inch long, in the intestine, where they fasten themselves 
to the intestinal wall, and not only suck blood themselves, but 
also cause considerable free bleeding from the wounds which 
they make. The eggs, which are laid in the intestine, do not 
there develop, owing to lack of oxygen, but hatch soon after 
the feces are voided, and the young worms then pass through 
several stages of growth in moist earth or mud. 

Until recently it was believed that human infection resulted 
from drinking water containing the young worms, or by get- 

1 Naish, Pub. Health, Lond., 1909-10, XXIII, 168; Sandilands, Proc. 
Roy. Soc. Med. 1910, III, Epidem. Sec, 109. 

2 Stiles, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. 
No. 10, 1903. 



INFECTION BY CONTACT 145 

ting them onto fingers or into food, and so into the mouth. 
It was first suggested by Looss in 1898 that infection might 
take place through the skin, and he believed that he had 
himself become infected in that way. In 1901 he proved the 
correctness of his surmises by experiments. Later Grassi, 
Pieri and Noe placed a few drops of water containing worms 
upon the skin, but only one of the three became infected. 
In 1902 Looss successfully repeated his experiments. It had 
meantime been noticed by Bentley and Boycott and Haldane 
that dermatitis was apt to be found in regions where the 
disease prevailed, and it was suspected that it might be due 
to the passage of the worms through the skin. Smith 1 showed 
that by placing infected earth on the arm, not only was infec- 
tion caused, but there resulted a dermatitis at the site of the 
application. Ashford, whose careful study of the disease 
in Porto Rico, and whose brilliant success in curing its vic- 
tims give his opinion great weight, believes that the skin 
is by far the most important avenue by which the worms 
infect the body. 2 Uncinariasis is, then, par excellence, & dis- 
ease due to contact infection. 

Fortunately the disease is usually easily curable under 
medical treatment, and the freeing of individuals from worms 
by this treatment is necessarily an important part of the 
prevention of the disease. It is evident from the mode of 
infection that the pollution of the soil with human feces is 
the principal factor in the spread of the disease. Properly 
constructed privies or water-closets, with the ultimate dis- 
posal of the fecal matter by deep burial, or some other means 
to prevent the pollution of the upper layers of the soil, are 
the essentials of prophylaxis. 

Contact Infection less Easy in Some Diseases than in 
Others. — Gonorrhea is a disease in which the infecting secre- 
tion is not likely to be much handled, and when it occurs 

1 Smith, C. A., J. Am. M. Ass., Chicago, 1905, XLV, 1142. 

2 Ashford, Rep. of Commission on Study and Treatment of 
"Anemia" in Porto Rico, 1904, 37. 



146 THE SOURCES AND MODES OF INFECTION 

in young children the secretion is often received on a diaper. 
Yet it has been shown in the preceding pages that infantile 
gonorrhea is spread exclusively by contact infection. Al- 
though the children themselves take little part in the spread 
of the disease in hospitals where they are isolated from one 
another, and although nurses and physicians have been shown 
the danger of carrying the disease, and have been instructed 
to take the greatest precautions, yet this disease may be 
maintained for months in an institution solely by means of 
infection borne on thermometers, syringes, etc., but particu- 
larly on the hands of attendants. 

In typhoid fever the bacilli are contained in the feces and 
urine, which even careless people are supposed to avoid touch- 
ing. Nevertheless it appears that the fingers of careful people, 
and even of trained nurses, are infected in this manner, and 
that transfer to the mouth with the subsequent development 
of typhoid fever results. There is much evidence that this 
mode of transference is an important, if not the most 
important, factor in the spread of this disease. 

Contact with Saliva. — If contact infection is important 
in such diseases as gonorrhea, typhoid fever, dysentery and 
cholera, in which the infecting material is not constantly at 
hand, and is usually strenuously avoided, how much more 
important must this mode of transference be in diseases in 
which the specific germs are found in the secretions of the 
nose and mouth or in the sputum. 

Danger from Fingers. — Probably the chief vehicle for 
the conveyance of nasal and oral secretion from one to another 
is the fingers. If one takes the trouble to watch for a short 
time his neighbors, or even himself, unless he has been par- 
ticularly trained in such matters, he will be surprised to note 
the number of times that the fingers go to the mouth and 
the nose. Not only is the saliva made use of for a great 
variety of purposes, and numberless articles are for one reason 
or another placed in the mouth, but for no reason whatever, 
and all unconsciously, the fingers are with great frequency 



INFECTION BY COX TACT 147 

raised to the lips or the nose. Who can doubt that if the 
salivary glands secreted indigo the fingers would contin- 
ually be stained a deep blue, and who can doubt that if 
the nasal and oral secretions contain the germs of disease 
these germs will be almost as constantly found upon the 
fingers? All successful commerce is reciprocal, and in this 
universal trade in human saliva the fingers not only bring 
foreign secretions to the mouth of their owner, but there ex- 
changing them for his own, distribute the latter to everything 
that the hand touches. This happens not once but scores 
and hundreds of times during the day's round of the indi- 
vidual. The cook spreads his saliva on the muffins and rolls, 
the waitress infects the glasses and spoons, the moistened 
fingers of the peddler arrange his fruit, the thumb of the milk- 
man is in his measure, the reader moistens the pages of his 
book, the conductor his transfer tickets, the " lady " the 
fingers of her glove. Every one is busily engaged in this dis- 
tribution of saliva, so that the end of each day finds this 
secretion freely distributed on the doors, window sills, fur- 
niture and playthings in the home, the straps of trolley cars, 
the rails and counter and desks of shops and public buildings, 
and indeed upon everything that the hands of man touch. 
What avails it if the pathogens do die quickly? A fresh 
supply is furnished each day. 

Drinking Cups. — Another important vehicle of transfer 
must be the common drinking cup. Davison 1 estimated that 
there were as many as 20,000 epithelial cells on a drinking 
glass that had been in use in a school for nine days, which 
well illustrates the amount of infection which may be thus 
carried. Cars, steamboats, hotels, schools, offices, factories, 
theaters, churches, all provide a common vessel from which 
large numbers of persons drink, thus furnishing an almost 
ideal method by which perfectly fresh saliva may be trans- 
ferred from one to another. Hundreds of thousands of 
persons must be each day in this manner exchanging the 

1 Davison, Tech. World Mag., Chicago, 1908, IX, 623. 



148 THE SOURCES AND MODES OF INFECTION 

secretions of the mouth. When traveling in the steam cars I 
have noted the shocked expression on the face of passengers 
as a fashionably dressed woman was seen to allow her pug 
dog to drink from the common glass, — not a pleasant thing, 
of course, but infinitely less dangerous than for the woman to 
drink from it. She might have tuberculosis, or carry diphthe- 
ria bacilli, or perhaps even have mucous patches on her lips. 

Other Kinds of Contact. — r Besides the moistening of the 
fingers with saliva and the use of the common drinking cup, 
the mouth is put to numberless improper uses which may 
result in the spread of infection. It is used to hold pins, 
string, pencils, paper and money. The lips are used to 
moisten the pencil, to point the thread for the needle, to wet 
postage stamps and envelopes. Children "swap" apples, 
cake and lollipops, while men exchange their pipes and women 
hatpins. Sometimes the mother is seen "cleansing" the 
face of her child with her saliva-moistened handkerchief, 
and perhaps the visitor is shortly after invited to kiss the 
little one. 

Children have no instinct of cleanliness, and their faces, 
hands, toys, clothing and everything that they touch must 
of necessity be continually daubed with the secretions of the 
nose and mouth. It is well known that between the ages of 
two and eight years children are more susceptible to scarlet 
fever, diphtheria, measles and whooping cough than at other 
ages, and it may be that one reason for this is the great 
opportunity that is afforded by their habits at these ages 
for the transfer of the secretions. Infants do not of course 
mingle freely with one another, and older children do not 
come in such close contact in their play, and they also begin 
to have a little idea of cleanliness. 

Contact Dangerous because of Missed Cases. — A little 
observation and reflection will show that the ways are num- 
berless in which fresh secretion of nose and mouth is passed 
from person to person. Enough has been written to demon- 
strate that the opportunities for contact infection are suffi- 



INFECTION BY CONTACT 149 

ciently numerous to account for the spread of the contagious 
diseases without invoking any other mechanism. The chief 
objection to this view is that while it is true that there is a 
considerable interchange of secretions, and even of excretions, 
between human beings, it is between well persons, and not 
between the sick and the well. That this objection is unten- 
able is amply demonstrated by the evidence presented in 
Chapter II. There can no longer be the slightest doubt that 
there are large numbers of mild and unrecognized cases of 
infectious disease mingling freely with the public, and that 
in some diseases, and perhaps in most, there are also larger 
numbers of perfectly well carriers who also are unknown. 
These unrecognized foci are clearly numerous enough to 
cause, by their contact with others, the recognized cases. The 
transfer of the disease by fairly direct means is so obvious 
and easy that there is no necessity for invoking the agency of 
other and more circuitous modes of dissemination. Indeed 
it is sometimes said that the arguments here presented prove 
too much, and that if carriers were as numerous, and contact 
with them as frequent, as is here alleged, none could escape, 
and infectious disease would be more common than it is. 
But, as was stated in Chapter II and on page 111, infection 
does not take place so readily as is generally believed. This 
is demonstrated clinically, and the reasons are apparent. 
There are often long intervals in which carriers are not elimi- 
nating the pathogenic organism, and the saliva may not con- 
tain the germs, even when they are in the throat and nose. 
Germs are not evenly distributed through saliva, sputum or 
feces, and the particle transferred may be free from them. 
The infective material is often small in amount and spread 
in a thin layer, and the contaminated organisms speedily die. 
Lastly, small numbers of pathogens are often, perhaps usu- 
ally, destroyed by the body. We must believe that usually 
continued or somewhat massive infection is necessary to cause 
disease, but that nevertheless sometimes a single infection 
with a very small number of germs suffices. The number of 



150 THE SOURCES AND MODES OF INFECTION 

unrecognized foci of infection in human beings, the oppor- 
tunities for contact infection, and the natural obstacles to 
successful infection, appear admirably to explain many other- 
wise inexplicable phenomena of epidemiology. 

Bacteria in Mouth. — There has been comparatively little 
effort made to determine by observation the frequency with 
which the common pathogens are actually found in the secre- 
tions of the nose and mouth and on the fingers and ob- 
jects which can serve as vehicles of contact infection. It 
is assumed, and I think with warrant, that the germs of 
many of our common diseases are thus widely distributed, and 
the assumption corresponds with clinical and epidemiological 
facts. But the subject is of such importance that it is very 
desirable that we should have something besides assumptions, 
and that more numerous observations should be made as to 
the presence of pathogenic bacteria in the secretions and 
upon and near human beings. 

On Hands. — Reference has been made in this chapter, 
page 137, to the finding of colon and typhoid bacilli on the fin- 
gers, but the examinations have been very few. Pus-forming 
organisms have their natural habitat on the mucous surfaces 
and in the skin, and the experimental work of the surgeons in 
improving their technique has demonstrated a very wide dis- 
tribution, and has shown the tremendous importance of con- 
tact infection, which they have now learned most successfully 
to avoid. 

Bacteria on Cups, Pencils. — Vincenzi l found diphtheria 
bacilli in the holy water in a church font. Kinyoun, 2 while 
searching for pathogens in railway cars, found diphtheria 
bacilli once on the woodwork and once on a drinking glass, 
though eighty-three other swabbings were negative. Forbes, 
in Rochester, found them upon a drinking glass which was 
believed to have been the cause of a small outbreak. This 
observation has been frequently referred to, and though I 

1 Vincenzi, Semaine med., 1898. 

2 Kinyoun, Med, News, N. Y., 1905, LXXXVII, 193. 



INFECTION BY COX TACT 15t 

have not been able to find Forbes' original article, Dr. Goler, 
the present health officer of Rochester, informs me that the 
facts are as reported. Williams 1 recovered diphtheria bacilli 
from pencils moistened by the lips of children sick with the 
disease. The observations referred to in the chapter on 
fomites show that the germs of this disease are rarely found 
on fomites and then only on objects that have been recently 
and grossly infected. 

Tubercle Bacilli in Mouth. — Not only are tubercle bacilli 
found in enormous masses in the true sputum, but they 
are often present in the saliva as well. Neild and Dunkley 2 
found them in saliva from the tip of the tongue in 29 of 50 
cases of pulmonary tuberculosis. Park found them in the 
saliva of 10 of 15 cases, 3 and refers to Moller recovering them 
in 3 of 20 cases. Le Noir and Camus 4 found virulent 
tubercle bacilli in the nose as well as from the mouth of 
tuberculous cases. 

Pathogenic Bacteria on the Hands. — With the present 
habits of human beings these germs must be constantly trans- 
ferred to the fingers, and to a lesser degree to everything that 
the fingers touch. Graziani 5 found tubercle bacilli on the 
hands of 4 of 8 tuberculous patients, and on 3 of them 3 
hours after washing with soap and water. He also obtained 
the bacilli from the hands of 4 out of 6 non-tuberculous 
patients. After shaking hands with tuberculous patients he 
was able several times to recover the bacilli from his own 
hands. Baldwin found bacilli on the hands of patients in 
the Adirondack Sanatorium. They did not use handker- 
chiefs. Of 10 patients seen in private practice 8 had tubercle 

1 Williams, Scientific Bull. 2, 1895, Health Dept., N. Y. City, 14. 

2 Xeild and Dunkley, Lancet, Lond., 1909, I, 1096. 

3 Park, Sixth Internat. Cong, on Tuberc, Wash., 1908, I, 157. 

< Le Noir and Camus, Comp. rend. Soc. de biol., Par., 1908, LXV, 464. 

5 Graziani, Ann d' Ig. Sper., XV, 709, referred to by Rosenau, Sixth 
Internat. Cong, on Tuberc, Wash., 1908, I, 28. 

6 Baldwin, Tr. Am. Climat. Ass., 1898, XIV, 202. 



152 THE SOURCES AND MODES OF INFECTION 

bacilli on their hands. The other two were exceptionally 
careful. Preisich and Schiitz x found tubercle bacilli on the 
hands of children in a children's hospital at Budapest. Of 
66 examinations of the dirt from under the finger nails 14 
were positive under the microscope, but owing to the death 
of the animals from sepsis their virulence was not demon- 
strated. Of the 14 positive cases, 11 had tuberculosis, or 
were associated with it, while of the 52 negative cases only 
5 were associated with tuberculosis. Dieudonne 2 by inocu- 
lation demonstrated tubercle bacilli on the hands of 2 of 
15 children. In this connection may be mentioned the 
experiment of Schumburg, 3 in which he rubbed an ose of a 
culture of bacteria on his hands, and recovered the germs 
after 15 and 16 handshakes. Ostermann, 4 on the other hand, 
does not consider contact infection of much importance in 
tuberculosis. While he recovered tubercle bacilli from the 
hands of 7 of 14 phthisical patients and from 1 attendant, 
he obtained them only 4 times from 42 children living in 
tuberculous families and 2 times from the floors occupied by 
these families. He does not find that bacteria are transferred 
from hand to hand as readily as have other observers. He 
also made a few cage experiments with guinea pigs to show 
that infection by contact is less effective than infection by 
air. 

It scarcely needed the experiments of Annett at Liverpool 5 
and Higgins 6 at Birmingham to show that virulent tubercle 
bacilli may be found in the sputum on sidewalks, or those of 
Dixon 7 to demonstrate that they may be swept up on the 
skirts of ladies' dresses. 

1 Preisich and Schiitz, Berl. klin. Wchnschr., 1902, XXXIX, 466. 

2 Dieudonne, Munch, med. Wchnschr., 1901, XLVIII, 1439. 

3 Schumburg, Ztschr. f. arztl. Fortbild., Jena, 1905, II, 567. 

4 Ostermann, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., 1908, LX, 375. 
6 Annett, Thompson Yates Laboratory Rep., 1901-02, IV, Pt. 2, 

359. 

6 Higgins, Pub. Health, Lond., 1909-1910, XXIII, 100. 

7 Letter from Dr. Samuel A. Dixon to author. 



INFECTION BY CONTACT 152 

In Communion Cups. — Anders ' found tubercle bacilli in 
the dregs from communion cups in a Philadelphia church, and 
Moller 2 from the communion cup of a sanatorium chapel. 
Davison 3 found them on a glass used for some weeks in a 
high school. He also demonstrated pneumococci. Klein 4 
obtained a positive tuberculous reaction once after inocula- 
tion of the swabbings of six telephones, although on twelve 
telephones on another occasion 5 he was unable to find either 
diphtheria or tubercle bacilli, and Hill 6 was unable to find 
either bacillus on twenty-four mouthpieces of lung-testing 
machines in Boston. Huhs 7 found tubercle bacilli on napkin 
rings in the sanatorium at Stadtwald, but did not find them 
on the spirometer which was in daily use. Price 8 used some 
water in which sanatorium dishes had been washed to 
inoculate eight guinea pigs, all of which died of tuberculo- 
sis. Washings from dishes which had been first washed in 
the ordinary way showed no bacilli. 

Contact Chief Mode of Infection. — Since it is true that 
pathogenic organisms begin to die or lose their virulence when 
thrown off from the body, we are forced to conclude that the 
closer the relationship in time and space with the bearers of 
the germs, the greater the chance of infection. Now that 
the number of unknown foci of infection and the oppor- 
tunities for direct transfer of secretions have been demon- 
strated, the deduction is certainly permissible that contact 
infection is more important than the more indirect infection 
by fomites or by air. 

We are also compelled by inductive methods to place the 
greatest emphasis upon contact infection. In the chapter on 

1 Anders, J. Am. M. Ass., Chicago, 1897, XXIX, 789. 

2 Moller, Deutsche med. Wchnschr., 1905, XXXI, 548. 

3 Davison, Tech. World Mag., Chicago, 1908, IX, 623. 

4 Klein, Lancet, Lond., 1908, I, 1862. 

5 Ref. J. Am. M. Ass., 1905, XLIV, 1866. 

6 Hill, Rep. Bd. Health, Boston, 1906, 91. 

7 Huhs, Ztschr. f. Tuberk. u. Heilstattenw., Leipz., 1906, IX, 396. 
s Price, Sixth Internat. Cong, on Tuberc, Wash., 1908, I, 167. 



154 THE SOURCES AND MODES OF INFECTION 

infection by fomites, and particularly in that on infection by 
air, much evidence is presented to show that infection usually 
does not take place unless contact is fairly close. The views 
here presented as to the great importance of contact infec- 
tion, and the comparatively slight importance of air infection 
and fomites infection, gradually developed after considera- 
tion of much experimental and epidemiological evidence. 
The two facts which more than all others have contributed 
to these views have been the restriction of scarlet fever and 
diphtheria to single families in the same house, and the suc- 
cess of certain hospitals in preventing cross infection, when 
contact infection is strictly guarded against. 

Disease Spreads in Dwellings only by Contact. — The 
rarity with which scarlet fever and diphtheria pass from 
one family to another in the same house has already been 
alluded to, but it is worth considering again. Of 4306 other 
families in Providence living in the same house with a case 
of scarlet fever, only 295, or 6.8 per cent, were later invaded 
by the disease. This includes all families, whether careful 
or careless, and whether or not the initial case was removed 
to the hospital; but as less than 10 per cent of the cases 
have been removed to the hospital during the 23 years 
covered by the figures, hospital isolation can have been of 
little moment. This amount of infection is surprisingly small, 
and of itself indicates very strongly that close and intimate 
contact is usually necessary for the extension of this disease. 
A further study of the facts indicates this still more clearly. 
During the last 5 years, scarlet fever has extended to 118 
of 1888 other families, or 6.3 per cent. In 54, or 22 per cent, 
of the cases infection occurred during the first two weeks, of 
which 37 were during the first week. Most of these cases 
during the first two weeks probably derived their infection 
from the first family before the disease was recognized. Only 
24 second families developed their infection after the end of 
the second week and while the warning sign was on the house. 
This is the time when the patients are desquamating and 



INFECTION BY CONTACT , 155 

when the disease is popularly believed to be most infectious. 
These 24 cases are 1.3 per cent of the 1888 other families in 
the infected houses. As in a number of these cases there was 
known to be considerable communication between the fami- 
lies, it seems to be certain that in an ordinary tenement 
house scarlet fever is not readily carried from one family to 
another, and that effective isolation is comparatively easy. 
In fact, everything goes to show that two or more families 
may live in the same house, using hallways, doors, and even 
water-closets in common, without scarlet fever extending 
from one to the other. All that is necessary is that there 
shall be absolutely no visiting between the families, and that 
the children shall never meet in play. I do not know that 
similar data have been collected elsewhere, but Cameron 1 
has shown by his study of "return" cases of this disease 
that in many instances the infecting case may remain in the 
family for some time, providing there is no direct contact 
with the well persons. 

Diphtheria is as little likely to extend from family to family 
without direct contact as is scarlet fever. During the last 
twenty-one years, in Providence, of 3667 other families living 
in a house with diphtheria, only 263, or 7.2 per cent, were 
invaded by the disease. During the five years 1904 to 1908, 
of 1648 other families, 114, or 6.9 per cent, have acquired the 
disease. Of these, only 38, or 2.3 per cent, were attacked after 
the first week of the initial sickness and before the warning 
sign was removed. As was shown above, many of these infec- 
tions are due to the fact that the first case is not recognized 
and hence the different families in the house continue to visit 
one another; or in some instances to the fact that persons in 
the second family carry the bacilli for a time without being 
sick. Probably a large part of the infections during the first 
week take place before the disease is recognized, so that it 
seems very probable that less than 2 and perhaps less than 

1 Cameron, Rep. on Return Cases of Scarlet Fever and Diphtheria, 
Lond., 1901-02, 98. 



156 THE SOURCES AND MODES OF INFECTION 

1 per cent of families living in a house with a case of diph- 
theria contract the disease while the warning sign is on the 
house. I have given particular attention to the cases of diph- 
theria arising in other families in the house while the warning 
sign remained on the apartment where the disease first ap- 
peared, and almost always there is known to be direct inter- , 
course between the families. Contact infection, then, seems 
to be necessary for the transfer of diphtheria from one family 
to another living in different apartments of the same house. 

Disease spreads in Hospitals only by Contact. — Another 
strong reason for this view that contact infection is the chief 
mode of extension for the common contagious diseases is the 
success of certain hospitals in preventing cross infection by 
minimizing in every way the opportunities for infection by 
contact. The Parisian hospitals, particularly the Pasteur 
Hospital, have been leaders in demonstrating the success of 
this method. In most hospitals for contagious diseases great 
effort is made to prevent cross infection by separating the 
different diseases to a considerable distance, since the theory 
prevails that air-borne infection is the chief mode of spread. 
This view so dominates hospital practice that numberless 
ways escape notice by which disease is spread by very direct 
contact, with the result that in most hospitals cases of cross 
infection are continually developing. 

French Hospitals. — The French seem to have been the 
first to appreciate the importance of guarding against contact 
infection, and an interesting account of the efforts made is 
given by Grancher, 1 who was one of the pioneers. Strict 
methods of "antisepsie medicale," as Grancher calls it, were 
introduced, and it was found possible to care for patients 
with different diseases even in a common ward with far less 
danger of transfer than before. He employed wire screens 
around the beds to impress upon the nurses the necessity for 
guarding against infection by contact. During the years 

1 Grancher, Cong. Internat. de med., XIII., C.-r. Par., 1900, Sec. 
de m6d. de l'enfance, 478. 



INFECTION BY CONTACT 157 

1890 to 1900, 6541 patients were treated in Grancher's wards, 
and diphtheria was introduced 43 times, but only once did 
a case develop in the wards. Scarlet fever was introduced 
19 times, and 7 cases developed in the wards. Less suc- 
cess was obtained in isolating measles, but infections were 
reduced two-thirds. Grancher was satisfied that even this 
disease was spread by contact. He believed that in clean 
wards infection is rarely air-borne; it is "objective," not 
" atmospheric." In several other French hospitals the impor- 
tance of preventing contact infection has been realized. In 
some of them isolation is made easier by placing the patients 
in separate rooms or cubicles; in some, partitions are placed 
between the beds. These partitions may be full height, or 
may stop short of the floor, and reach only just above the 
head. Sometimes screens only are used. In 1897 the Min- 
turn Hospital in New York, a small private hospital, was 
built to provide isolation in separate rooms for cases of scarlet 
fever and diphtheria. But the most notable example of the 
new method is the Pasteur Hospital in Paris, opened in 1900. 
The success of these various hospitals in preventing cross 
infection is correlated, not with the amount of isolation as 
ordinarily understood, but with the care with which aseptic 
measures are carried out by the attendants. The cubicles, 
partitions and screens certainly cannot prevent infection if 
the nurses without taking proper precautions pass from one 
case to another. This is shown by the constant development 
of cross infection in the ordinary hospital. It was in the 
Pasteur Hospital that the principles of medical asepsis were 
first fully appreciated and carried out in a practical manner. 
The hospital consists of two pavilions with about fifty beds 
each, designed ostensibly, one pavilion for scarlet fever and 
one for diphtheria; but, as is shown below, all sorts of cases 
are admitted. For the care of all these " other diseases " 
and mixed and doubtful cases, twelve single rooms are pro- 
vided in each ward, all opening into a common corridor, the 
doors of which are usually left open. The same nurses look 



158 THE SOURCES AND MODES OF INFECTION 

after different diseases, often in adjoining rooms. The disci- 
pline of the hospital attempts to secure an entire avoidance 
of contact infection, and is remarkably successful. Yet the 
procedures are all very simple. The nurse always sterilizes 
her hands after waiting on the patient; she wears a gown, 
which is kept in the room, when anything is done which 
would be likely to infect her clothing. Nothing goes into the 
room except what is sterile, and nothing comes out without 
being at once sterilized. To train nurses sufficiently to take 
charge of a ward, two years are necessary, but the nurses 
whom I saw there were carrying out these details with the 
same precision and unconsciousness which are shown by the 
bacteriologist in his laboratory. 

English Hospitals. — The principles of aseptic nursing as 
applied to contagious diseases have been employed in a num- 
ber of places in England, as, for instance, in the North 
Eastern, South Western and London Fever hospitals in 
London, at Walthamstow and Manchester, and doubtless in 
other places. The methods adopted in the Monsall Hospital 
at Manchester, and described by Gordon, 1 are as follows: 

"The patient's bed in the general ward is surrounded with 
a screen covered with sheets, which are kept constantly wet 
with a weak solution of some disinfectant. The main pur- 
pose of this screen is to serve as a label, and to remind the 
nurses that certain precautions must be taken for the patient 
behind it. At the same time, I think the wet sheets may pos- 
sibly arrest infective particles that are projected against them 
in the acts of coughing and sneezing. The only other requi- 
sites are two glass shelves fixed on the wall behind the bed, 
and a locker or portable cupboard made of metal, with an 
enameled surface, which can easily be disinfected and kept 
clean. 

" The precautions to be taken by the nurses in attending 
patients behind this screen or ' barrier ' are printed on a 
card fixed to the screen, and are as follows: 

1 Gordon, Rep. on Health of Manchester, 1908, 154 



INFECTION BY CONTACT 159 

Rules in Manchester. — " Precautions to be Observed in 
the Nursing of Barriered Cases. 

"(1) Rubber gloves are to be worn by the Nurse for all 
manipulations connected with the case, including the han- 
dling of clothes. The gloves are to stand in a bowl of 1 in 400 
Izal solution. 

" (2) The following utensils are to be marked and kept on 
the glass shelves or in the locker provided: 

Spatula To be kept completely 

Nozzles immersed in a 1 to 

Clinical Thermometer J 400 Izal solution. 
At least two bowls. 
All feeding utensils (plates, spoons, forks, etc.). 

"(3) A plentiful supply of wet swabs, with a bowl contain- 
ing Izal solution to receive these when used, is to be kept on 
the locker. Handkerchiefs or muslin squares are not to be 
employed. 

"(4) No toys or books that have once been used inside 
the barrier are to be taken outside it except to be destroyed. 

" (5) In every case a square of jaconette is to be placed on 
the pillow slip, and over this a piece of muslin; the latter is 
to be renewed whenever soiled. 

"(6) An overall is to be worn by the Nurse whenever 
either the patient or the clothes are handled. This is to be 
kept inside the barrier." 

The success of the methods described in the preceding 
pages is well shown by the published figures. At the 
Pasteur Hospital from October 1, 1900, to April 19, 1903, 
the following cases were received: 

Diphtheria 443 Scarlet fever 92 

Sore throat 166 Erysipelas 163 

Smallpox 524 Phlegmon of tonsil 29 

Chicken pox 55 Other diseases 219 

Measles 126 Mothers with infants.. 192 



160 THE SOURCES AND MODES OF INFECTION 

Such a combination furnishes a remarkably fertile field for 
cross infections. During the next year about 750 cases were 
admitted. 1 

During this whole period the only cases which developed 
in the hospital were 5 of smallpox, 2 of erysipelas and 1 of 
diphtheria. Dr. Loiseau writes me that since 1904 the per- 
centage of cross infections has been less than 0.1 per cent. 
At the Minturn Hospital in New York there has been no in- 
stance of infection in the hospital. At the Monsall Hospital 
in Manchester in 1908 a large number of persons admitted 
with mistaken diagnosis were cared for in the wards by the 
methods described without contracting the disease, and a 
number of cases of mixed infection were cared for in the open 
wards without infecting others, except in one instance when, 
owing to a mistake in orders, " barrier " isolation was not 
promptly instituted. A letter just received from Dr. Arnold, 
who has succeeded Dr. Gordon at Monsall, states that in 
order that the patient may see and be seen, and to avoid 
the dampness of the wet sheet, he has substituted a tape 
which as effectually prevents the mythical aerial flight of the 
germs, or, to speak literally, equally well reminds the nurse 
that she must be clean. 

Is Tuberculosis Air-borne ? — It is assumed that tuber- 
culosis, as it occurs in human beings, is usually an air-borne 
disease, and as will be shown on another page, there is more 
reason for such an assumption concerning this than concern- 
ing most diseases. Yet there is in certain quarters a growing 
tendency to attribute to contact infection more importance 
than formerly. Yet it must be confessed that most writers 
on this disease lay no emphasis on contact infection, and 
some scarcely mention it. Cornet, 2 in speaking of kissing, 
the most direct means of contact infection, says that it is 
incredible that tuberculosis should be transmitted in this 
way, for the saliva is ordinarily germ free, and the germs if 

1 Martin, Bull, med., Par., 1904, XVIII, 251. 

2 Cornet, Nothnagel's Encyclopedia, Tuberculosis, 187. 



INFECTION BY CONTACT 161 

present would not be carried to the lungs. Cornet's first 
contention is certainly not correct, for Neild and Dunkley, as 
before mentioned, found tubercle bacilli on the tip of the 
tongue of phthisical patients examined during intervals of 
freedom from cough. They also report cases of lupus, due in 
all probability to inoculation with saliva, and refer to others 
reported by Wild. 1 

There has been little experimental work to determine the 
part played by contact infection in tuberculosis. The work 
of Bartel and Spieler 2 indicates that guinea pigs exposed 
under natural conditions to contact with the members of a 
tuberculous family more often develop the disease than do 
animals exposed merely to the air of the room, while the 
experiments of Packard, though inconclusive, indicate little 
difference. 

Infection by Alimentary Tract. — There seems to be evi- 
dence that the tonsils may be the seat of infection in many 
cases of tuberculosis. Harbitz 3 has very forcibly called atten- 
tion to the probability that tubercle bacilli frequently gain 
access to the body through the tonsils. He examined the 
tonsils and lymphatic glands of a large number of children, 
and found latent tuberculosis in many of the tonsils, and 
latent bacilli in the cervical glands in 17 instances, much more 
often than in the mesenteric glands. He thinks that a more 
careful study of the tonsils and lymph nodes would reveal 
much latent tuberculous infection, and he thinks that a con- 
siderable amount of infection takes place through the tonsils. 
Harbitz mentions Grawitz, 4 Aufrecht 5 and Beckmann as sup- 
porting this view. Ravenel and Reichel 8 review much litera- 
ture, and refer to Wood's experimental infection of swine 

1 Wild, Brit. M. J., 1899, II, 1353. 

2 Referred to in the chapter on infection by air. 

3 Harbitz, J. Infect. Dis., Chicago, 1905, II, 143, and especially 198. 

4 Grawitz, Deutsche med. Wchnschr., 1901, XXVII, 711. 

5 Aufrecht, Verhandl. d. deutsch. path. Gesellsch., Berl., 1901-02, 
IV, 65. 

6 Ravenel and Reichel, J. Med. Research, Bost., 1908, XVIII, 1. 



162 THE SOURCES AND MODES OF INFECTION 

through the tonsils, the course of the bacilli being apparently 
through the submaxillary and cervical glands. Benome l 
caused infection in animals through the mouth and pharynx. 
Bandelier 2 finds primary tuberculosis of the tonsils not so rare 
as is generally believed, but he does not consider the tonsils 
as a frequent starting point of phthisis. Mohler and Ravenel 
from experiments and observations consider the mouth as 
a frequent site of infection in the tuberculosis of hogs. 

Contact Infection in Tuberculosis. — The nose also may 
be the seat of infection. Cornet, 3 by applying infective ma- 
terial by means of a feather to the nasal mucous membrane 
of guinea pigs, was able to produce disease of the nose and 
submaxillary glands. Renshaw 4 was able in the same way 
to infect seven of eight animals. As tubercle bacilli are nu- 
merous upon the hands of consumptives and upon various 
articles used by them, it is evident that fresh bacilli must be 
frequently carried to the mouth and nose of persons near by, 
and may either infect directly through the mouth, nose and 
pharynx, or may be swallowed and enter the circulation 
through the lower part of the alimentary canal. The only 
question is, How frequently does this happen? As was stated 
above, it is the opinion of many that it is a very common 
mode of infection. Moore 5 is of the opinion that in cat- 
tle tuberculosis is spread chiefly by the animals licking 
one another, and by their eating and drinking from the 
same vessels. Bartel 6 believes that infection by pharynx, 
stomach and intestines is more common than has been sup- 
posed, in which view he supports Weichselbaum, 7 Volland, 8 

1 Benome, Ref. J. Am. M. Ass., Chicago, 1907, XLIX, 888. 

2 Bandelier, Beit. z. Klin. d. Tuberk., Wiirzb., 1906, VI, 1. 

3 Cornet, Nothnagel's Encyclopedia, Tuberculosis, 154. 

4 Renshaw, J. Path, and Bacteriol., Lond., 1901, VII, 142. 

5 Moore, Conference of Sanitary Officials, N. Y., 1907, 37. 

6 Bartel, Sixth Internat. Cong, on Tuberc, Wash., 1908, I, 95. 

7 Weichselbaum, Festsch. VI Konf. Internat. Tuberk., Wien u. 
Leipz., 1907. 

8 Volland, Berl. klin. Wchnschr., 1899, XXXVI, 1031. 



INFECTION BY CONTACT 163 

Kavacs 1 and Preisich and Schutz. 2 Among others who at- 
tribute much importance to contact infection may be men- 
tioned Wassermann, 3 Calmette and Landouzy. 4 

Certainly the opportunities for the direct transfer of fresh 
moist infective material in the home of a phthisical patient 
must be very great, while the chance of the infective material 
becoming dried, pulverized and, while still virulent, being car- 
ried to the pulmonary alveoli, must be comparatively small. 
Unless there is some good reason to think otherwise, one 
would naturally attribute to contact infection the chief role 
in the extension of this disease, at least in the family. The 
only objection is offered by the pathologists, many if not 
most of whom affirm that the evidence points to direct infec- 
tion of the lungs by the inspired air. There are, however, 
many able experimenters who think otherwise, and who main- 
tain that tubercle bacilli may enter the body at various points 
and reach the lungs through the lymph channels. It is impos- 
sible for the writer properly to weigh pathological evidence, 
but that the question is still sub judice must be admitted. 
Under the circumstances it seems to be wise to assume 
as a working hypothesis that contact infection is a factor of 
great importance in the causation of human tuberculosis. It 
is certainly essential to guard against such infection in every 
way, and from a person who does thus conduct himself in a 
cleanly manner at all times, diffusion of the disease through 
the air would be impossible. Undue emphasis laid upon the 
invisible and therefore terrifying infection in the air has done 
more than anything else to develop the unfortunate phthisi- 
phobia which so often renders miserable the life of the tuber- 
culous, and seriously interferes with rational measures for the 
restriction of the disease. 

1 Kavacs, Zeiglers Beitrage zur. Path. Anat., 1906, XL. 

2 Preisich and Schutz, Berl. klin. Wschnschr., 1902, XXXIX, 466. 

3 Wassermann, Berl. klin. Wchnschr., 1908, Nr. 48. 

4 Calmette and Landouzy, Sixth Internat. Cong, on Tuberc, Wash., 
1908, I, 110. 



164 THE SOURCES AND MODES OF INFECTION 

Importance of Contact Infection. — I have sometimes been 
told that I lay too much emphasis on contact infection, but 
if it is the principal way in which disease spreads, too much 
emphasis cannot be placed upon it, and it seems to me that 
the evidence is that it is the chief mode of infection. Even 
if it is not so important as is here alleged, every one must 
admit that it is of considerable importance, yet until recently 
very little attention has been paid to it. If contact infection 
is the chief mode of extension of the contagious diseases, then 
defense against them becomes more largely a personal affair 
than we have been taught. We do not have to rely exclu- 
sively on the municipality for our protection, awaiting forced 
isolation, hospital construction, disinfection and the like, but 
can largely protect ourselves by keeping our fingers out of 
our mouths, and also everything else except what belongs 
there. It may not be possible to prevent all contagious sick- 
ness in this way, but some can be avoided, and perhaps most 
of it. Contact infection is avoided by personal cleanliness, 
and personal cleanliness is demanded by decency, good man- 
ners and refinement, as well as by hygiene. It is not much 
trouble to be decently clean, and it is not very expensive. 
It is a serious mistake to build an expensive isolation hos- 
pital that does not check disease, or to construct a filter when 
it is not needed; but no harm would be done if the views here 
presented should be found to be erroneous and people should 
learn to wash their hands and keep their fingers out of their 
mouths to no purpose so far as disease prevention is concerned. 
It seems certain that much can be done to prevent the spread 
of disease in the family and in hospitals, schools and institu- 
tions, if only personal cleanliness be insisted upon. Yet such 
cleanliness or medical asepsis is sadly neglected by physicians 
as well as by nurses. Rather strong preaching is needed 
when, as was referred to on another page, a typhoid nurse is 
detailed for the double duty of washing bedpans and preparing 
food. It is certainly necessary to insist somewhat strenuously 
on reform when such occurrences as the following take place. 



INFECTION BY CONTACT 165 

Disregard of Contact Infection. — Thus, at one of the finest 
hospitals in this country, with separate wards for scarlet fever 
and diphtheria, a considerable number of cases have arisen 
in the general wards. The germs were supposed to be air- 
borne, as it was said there was no other possible avenue of 
infection. When I saw the head nurse lick her finger to 
facilitate turning the bedside charts of diphtheria patients, I 
suspected that the principles of medical asepsis had not been 
entirely mastered. Called to see a case of scarlet fever in a 
well-to-do family, I found the door of the sick-room carefully 
hung with a sheet to keep the infection from the other chil- 
dren. After examining the throat with a spatula I handed 
the latter to the mother. She took it into the hall and put 
it on an upholstered sofa, and with her saliva-infected hands 
opened the door of an adjoining room. The attending physi- 
cian meanwhile sat on the bed and handled the patient, an 
entirely unnecessary proceeding at that time, and except for 
the example set him, would have forgotten to wash his hands 
before leaving. A certain hospital determined to copy in one 
of its wards the cubicle system of the French, but had so 
missed its essential features that I found doctors and nurses 
going from cubicle to cubicle feeling the pulse, smoothing the 
bedclothes, and handling dishes without even stopping to 
wash their hands. Meanwhile the screen was supposed to 
prevent the microbes from passing from bed to bed, and we 
all carefully wore gowns and caps so that the wicked little 
germ might not jump into our hair and then jump off again 
onto the next patient. In another fine hospital for conta- 
gious diseases, where great stress is laid upon ample space 
between different diseases so as to prevent cross infection, 
the superintendent was observed freely to touch articles about 
the ward, and handle the patients, and then go to the public 
office without even washing his hands. Such incidents could 
be multiplied indefinitely. The superintendent of another hos- 
pital invited another visitor and myself to eat ice cream from 
the same spoon as himself, which spoon was then replaced 



166 THE SOURCES AND MODES OF INFECTION 

in the freezer which was to supply the wards. I was most 
of all impressed with the fact that at the International Con- 
gress on Tuberculosis in 1908 a large number of the readers 
of papers moistened their fingers with their tongue when turn- 
ing the pages, and in each of the sections only one drinking 
glass was provided for all the speakers; and this continued 
without protest for a day or two. If the most distinguished 
investigators and health officials of the world, gathered to 
study the most important contagious disease, show no appre- 
ciation whatever of the importance of contact infection, it 
is certainly time for some one to be emphatic. 

Personal Prophylaxis. — The discovery that disease germs 
are rarely able to maintain themselves outside of the body 
clouded the hopes of those who expected by municipal house 
cleaning to " stamp out the zymotic diseases," and the later 
discovery of numerous missed cases and carriers has shown 
that isolation of the sick controls infection far less than was 
believed. These somewhat discouraging facts are to a large 
degree offset by what has been learned of the modes of 
infection. Formerly air infection was chiefly feared; now it 
appears that contact infection is of prime importance. For- 
merly dependence was placed upon the state to isolate and 
disinfect; now it appears that the individual can protect him- 
self, and as easily protect others if he chance to be infected. 
It is usually comparatively simple so to live as not to allow 
the secretions of others to come in contact with one's own 
mucous surfaces, and it is easy, and should be considered 
immoral, to allow one's own secretions to be so placed that 
they may infect another. Personal cleanliness is less expen- 
sive than municipal cleanliness, and is within the reach of all. 

Need of Education. — When one notes the utter disregard 
of medical asepsis shown in our hospitals and medical con- 
gresses, one is apt to feel that the education of the public in 
habits of personal cleanliness will take a very long time; but 
some encouragement is felt when it is remembered that it is 
not so very long ago that excrement was commonly thrown 



INFECTION BY CONTACT 167 

into the street and garbage was tossed under the tables of 
the great. It is only a few years since our sidewalks were 
necked with saliva, but now nineteen persons out of twenty 
are ashamed to be caught spitting on the pavement. Perhaps 
we may all soon learn to stop distributing our secretions so 
freely among our friends. 

Education in School. — As the avoidance of contact infec- 
tion is chiefly a personal matter, the present need is for educa- 
tion. First of all, the teachers in the medical schools and the 
staffs of hospitals must learn to appreciate the importance of 
this mode of infection. It is not unreasonable to hope that 
in a few years the schools and the hospitals will place as 
much emphasis on medical asepsis as they now do on surgical 
asepsis, and it is to these centers that we must look for the 
education of physicians, health officers and nurses. To edu- 
cate the general public is a more difficult matter. Some years 
ago Dr. Theobald Smith called my attention to the desirabil- 
ity of teaching school children something about the require- 
ments of personal cleanliness, and since then I have each year 
distributed to each school child the following " dont's " 

REMEMBER THESE THINGS. 

Do not spit if you can help it. Never spit on a slate, floor, 
or sidewalk. 

Do not put the fingers into the mouth. 

Do not pick the nose or wipe the nose on the hand or sleeve. 

Do not wet the finger in the mouth when turning the leaves 
of books. 

Do not put pencils into the mouth or wet them with the 
lips. 

Do not put money into the mouth. 

Do not put pins into the mouth. 

Do not put anything into the mouth except food and drink. 

Do not swap apple cores, candy, chewing gum, half-eaten 
food, whistles or bean blowers, or anything that is put into 
the mouth. 



168 THE SOURCES AND MODES OF INFECTION 

Never cough or sneeze in a person's face. Turn your face 
to one side. 

Keep your face and hands clean; wash the hands with soap 
and water before each meal. 

Providence, May, 1901. 

An explanatory circular is sent to the teachers, and of late 
a short account of the sanitary reasons for personal cleanli- 
ness has been distributed to children above the primary 
grade. Large printed copies of the " dont's " have been 
framed and hung in the schoolhouses. 

Much kindergarten work is of such a nature as to inculcate 
rather than discourage cleanly habits. Children work in com- 
mon in moist clay and sand, use the same " gifts" and toys 
and are brought into close contact in the games. Miss Bessie 
M. Scholfield, the supervisor of these schools in Providence, is 
now attempting, without any undue expense or violent change 
of methods, to employ kindergarten work as a means of teach- 
ing some of the principles of personal hygiene. 

Municipality should encourage Cleanliness. — Besides 
efforts that are directly educational the municipality can do 
much indirectly to encourage habits of personal cleanliness 
and to prevent the distribution of the secretions and excre- 
tions of the body. The common drinking cup is a most 
efficient means of such distribution, and it should be abolished 
in all schools and other public institutions. This has been 
done in many places, and individual cups or specially designed 
drinking fountains substituted. The example is now being 
followed by some railways, factories and shops. The states 
of Kansas, Michigan and Mississippi have forbidden the 
use of a common drinking glass on railways, and the Lacka- 
wanna and some other roads advertise as an attraction free 
cups of paraffin paper for each passenger. 1 Hundreds of 
churches have adopted the individual communion cup. The 
roller towel should go the way of the common drinking cup. 
1 J. of Outdoor Life, 1909, VI, 371, 



IXFECTIOX BY COXTACT 169 

People are more likely to keep clean if it is easy to do so. 
Hence the establishment of public baths may be considered 
a real sanitary measure. While compulsion can have little 
share in the campaign for cleanliness, certain prohibitions are 
entirely reasonable and feasible. Thus ordinances against 
spitting on the sidewalks and the floors of public places have 
done much to teach people to take proper care of their secre- 
tions. Reference has already been made to evidence that the 
abolition of privy vaults results in a decrease in typhoid fever. 
Privy vaults certainly encourage the improper disposal of 
excreta and general uncleanly habits. A good sewage system 
and the removal of vaults and cesspools do much to prevent 
contact infection, at least in the fecal-borne diseases. 



CHAPTER V. 

INFECTION BY FOMITES. 

Definition of Term. — As was shown in the preceding 
chapter, it seems very probable that contagious disease may 
often be caused by the quite direct transference of the germs 
from one person to another on such objects as cups, pencils, 
pipes, the fingers, etc. This mode of transference should 
properly be considered a form of contact infection. The term 
contact infection, as commonly used at the present time, does 
not necessarily imply the immediate touching of two persons, 
but it does imply the comparatively direct transference of 
quite fresh material from one to another. Although almost 
any object may in this manner be the bearer of infection, it 
would not ordinarily be considered as fomites. By fomites 
are usually meant infected objects which retain the infection 
for some time. A toy used by a diphtheria patient and sent 
to a distant town and there giving rise to the disease, the 
dress of a scarlet-fever patient put away for weeks or months 
and brought out only to cause another case, a library book 
carrying the infection of smallpox from one household to 
another, blankets loaded with typhoid bacilli in South Africa 
transferring infection to England, infected hides from Asia 
causing anthrax in Philadelphia, blank cartridges as the bear- 
ers of tetanus germs, and the various objects in a room lately 
occupied by a case of any contagious disease giving rise to 
the same affection in newcomers, would all be recognized as 
fomites. The cup which carries the moist saliva from one 
school child to another, the borrowed pencil which transfers the 
fresh syphilitic virus from lip to lip, and the urine-moistened 
closet seat which infects the fingers and then the mouth of 
the next user, are not thought of as fomites but as the neces- 

170 



INFECTION BY FOMITES 171 

sary media for that intimate mode of disease transference 
which is coming to be called contact infection. This dis- 
tinction between the two classes of bearers of infection is 
somewhat arbitrary, and not very definite, but is eminently 
practical. In this book, by infection by fomites is meant a 
transference of infecting material on objects under such con- 
ditions that considerable time elapses, days at least, usually 
weeks, sometimes months. 

Yellow Fever and Fomites. — If one takes up the older 
text-books on yellow fever it will be found that fomites were 
considered the most important means in the extension of this 
disease. The invasion of cities and countries was usually 
attributed to this mode of carriage. This was the general 
view up to, and indeed after, the discovery of the role played 
by the mosquito, and numerous instances of such transference 
are given. Thus the federal inspectors 1 attributed the out- 
break at Brunswick, Ga., to ballast brought from Cuba. The 
disease was supposed to have been carried from New Orleans 
to Havana by means of second-hand oyster buckets. 2 Lice- 
aga 3 gives instances of the transmission of yellow fever by 
a shipload of grain from New Orleans, by cloth spread out 
on the grass to dry, by general merchandise, by bagging, by 
clothing, and by ballast. Horlbeck 4 says that two persons 
at Key West contracted yellow fever from sleeping on a mat- 
tress that was brought from Cuba. 

Never so Transmitted. — In all these instances the evi- 
dence is the same : a locality has long been free from yellow 
fever, something is imported from an infected place and the 
disease develops. What could be clearer? The proofs that 
it is a fomites-borne disease were far more numerous and 
stronger for yellow fever than for almost any other disease. 

1 Rep. Surg. Gen. U. S. Mar. Hosp. Serv., 1893, II, 33. 

2 Report on Shipment of Merchandise, U. S. Mar. Hosp. Serv., 
Special Report, 1899, 9. 

3 Liceaga, Am. Pub. Health Ass. Rep., 1898, XXIV, 122. 

• Horlbeck, Am. Pub. Health Ass. Rep., 1897, XXIII, 436. 



172 THE SOURCES AN I) MODES OF INFECTION 

Yet we now know that yellow fever never was, nor could be, 
transmitted in any such way. Such a mistake, a mistake which 
cost millions upon millions because of the needless interrup- 
tion of commerce, and disinfection, should make us careful 
how on similar, but weaker, evidence we attribute importance 
to fomites as a means of infection in other diseases, and should 
lead us to inquire what proof there is that the long persist- 
ence of infection on things is a weighty factor in the trans- 
mission of disease. 

Smallpox. — It does not require much search in medical 
literature to find numerous instances of the alleged trans- 
mission of disease by fomites. Recent text-books and jour- 
nals are full of them. Welch and Schamberg 1 state that 
smallpox was brought to Philadelphia on cotton from the 
South, but the only reasons for thinking so were that there 
was much smallpox in the cotton region and none in Phila- 
delphia, and that the patient handled cotton. Not long since 
the health officer of a western city reported that the principal 
source of smallpox in that city was lumber, his assumption 
being based on the facts that there was much of the disease 
in the lumber camps, that the rough lumber was well fitted 
to carry contagion, and that in most families the first person 
attacked was engaged in some sort of woodworking. The 
above are fair samples of the kind of evidence on which the 
theory of fomites infection rests. Smith 2 reports that a man 
from Paris died in London of what was probably malignant 
smallpox. Two people who afterwards slept in the same bed, 
on different days, developed the disease, as did the girl who 
sorted at the laundry the soiled linen from this hotel. 

Scarlet Fever. — A recent writer in Public Health* reports 
six instances of house infection giving rise to scarlet fever, 
in one case nine months after the first patient was sick. The 

1 Welch and Schamberg, The Acute Infectious Diseases, Phila., 1905, 
160. 

2 Smith, Pub. Health, Lond., 1901-02, XIV, 211. 

3 Trotter, Pub. Health, Lond., 1906-07, XIX, 745. 



INFECTIOX BY F0M1TES 173 

only evidence was the recurrence of the disease in the house. 
Welch and Schamberg 1 quote from others reports of fomites 
infection in this disease. Boeck states that the hair of a 
scarlet-fever patient caused the disease twenty years after. 
Another physician caught the disease from a coat which he 
wore while attending a case a year and a half before. The 
health officer of Detroit 2 reports two cases due to infection 
from books which had been used by a patient some months 
before. Wende 3 states that quilts used by scarlet-fever 
patients in August, and put away without disinfection, 
caused the disease in November. The reports of the state 
board of health of Michigan 4 give instances of the per- 
sistence of the scarlet-fever virus for years in houses, letters, 
books, etc. 

Diphtheria. — Buckley quoted from the Newton, Vic- 
toria, Health Report an instance where a cornet used by a 
diphtheria patient was put away for four years, and was then 
found by some children, who contracted the disease from it. 
He gives another instance where the disease recurred in the 
house after a period of two years. At a time when Manila 
was absolutely free from diphtheria, an American child who 
had been there over a year received some Christmas presents 
from St. Louis, and was taken sick a few days later. Chris- 
tian 6 writes of the transmission of diphtheria on carpenters' 
tools which were sent from one shop to another. 

Cholera. — A number of instances of the transmission of 
cholera by soiled clothing are given in the Report of the 
Marine Hospital Service for 1893. 7 In nearly every instance 
the clothing was brought from foreign countries. Because 

1 Welch and Schamberg, The Acute Infectious Diseases, Phila., 1905, 
344. 

2 Rep. Bd. of Health, Detroit, for year ending June 30, 1903, 11. 

3 Buffalo San. Bull., Nov. 30, 1908. 

* Rep. St. Bd. Health, Mich., 1906, 134; 1907, 133. 

6 Pub. Health, Lond., 1906-07, XIX, 296. 

« Bull. N. Y. St. Board of Health, June, 1907, 5. 

7 Rep. Surg. Gen. U. S. Mar. Hosp. Serv., 1893, Vol. II, 353. 



174 THE SOURCES AND MODES OF INFECTION 

a company of soldiers had suffered from typhoid fever for 
two years, and the disease ceased on disinfecting the bar- 
racks, the outbreak was believed to have been due to room 
infection. 1 

Before weighing the value of this evidence it is perhaps 
worth while to consider some of the things which are most 
often alleged to serve as fomites. 

Infected Clothing. — From the time when the priest was 
directed how to detect leprosy in woolen and linen 2 to the 
present, clothing has been considered an important vehicle 
of infection. It is not to be doubted that disease germs may 
be carried on clothing. If clothing is soiled with a consider- 
able quantity of infected saliva, feces, urine or pus, and if 
while fresh, say within a few hours or days, it is brought in 
contact with susceptible persons, disease may result. If it is 
folded and put away in the dark, especially if it be in a damp 
place, it may remain infectious perhaps for months. But as 
bacteria as a rule die rapidly, and as there must be a sequence 
of gross infection, favorable conditions for survival, and con- 
tact with susceptible persons, it does not seem likely that 
disease is often caused in this way. 

Many instances are recorded, usually only of possible, rarely 
of probable, transference of disease by clothing. Of yellow 
fever more than of any other disease has this been alleged, yet 
we now know that such transmission of this disease is impos- 
sible. Many writers also report the spread of bubonic plague 
by means of clothing, but, as will be seen, the evidence is that 
plague is only under very exceptional circumstances carried 
by fomites. 

Typhus not carried in Clothing. — When typhus fever 
appeared in New York in 1892, from sixty to seventy-five 
officers of the health department were, according to Doty, 3 

1 Cited by Germane-, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 
1897, XXIV, 404. 

2 Leviticus, Chapter xiii, verses 47-59. 

3 Doty, Med. News, N. Y., 1905, LXXXVI, 730. 



INFECTION BY FOMITES 175 

more or less in contact with the cases, often in intimate con- 
tact; gowns were not used, and the officials went freely be- 
tween the patients and their own homes, and about their 
other business, yet no case of this disease could be traced to 
fomites infection. 

Butler 1 speaks of a parlor maid in a contagious-disease 
hospital who for six months had been in daily contact with 
nurses coming directly from scarlet-fever cases without change 
of clothes, but she did not contract the disease until exposed 
to an incipient case in the person of a nurse, when she 
promptly developed scarlet fever. This is only one illustra- 
tion of many of the failure of supposedly infected clothing 
to infect. 

Physicians rarely carry Disease. — In scarlet fever and 
diphtheria physicians are constantly passing from the sick to 
the well. Some of them take great precautions to avoid 
carrying the disease in their clothes, but the majority take 
few or none, — or at least did not until very recently. Yet 
records of their transmitting disease are extremely rare. For 
many years I was on the lookout for this mode of transference, 
and only once or twice found any evidence that the physi- 
cian was at fault. Even if the infection, say of diphtheria, 
can be traced to the physician, which is most likely, that the 
bacilli were carried from the sick to the well in his clothes, or 
even that they were on his unwashed hands, or that he had 
become a carrier and they were growing in his throat? The 
relative probability of the first hypothesis is so small that it 
may be dismissed. 

Infection by Clothing is Rare. — If the gross infection of 
clothing is only in rare instances the cause of disease, how 
little must be attributed to slight infection! A few droplets 
of tuberculous saliva, a slight smear of moisture from the 
lips of a diphtheria patient, will soon lose their virulence after 
exposure to light and air. But usually the visitor in a sick- 
room will escape all infection except the hypothetical floating 

1 Butler, Proc. Roy. Soc. Med., Lond., 1908, 1, Epidemiol. Sec., 225. 



176 THE SOURCES AND MODES OF INFECTION 

particles. The danger from this floating matter will be shown 
in another chapter to be a negligible quantity. It is the com- 
mon practice for physicians, nurses and visitors in a room 
occupied by a contagious case to wear a gown and cap. For 
physicians and nurses who are to move or lift the patient, or 
otherwise come into intimate contact with him, the gown is 
a reasonable protection against possible gross contamination. 
For the careless visitor too it may be useful. The cap is a 
useless frivolity. It is amusing to see how religiously it is 
worn, while no protection is given the feet, though Denny 
and Nyhen 1 have shown that infection by means of the shoes 
is bacteriologically possible, while the aerial infection of the 
hair has never been demonstrated and is highly improbable. 
More than once have I seen a physician don his cap to keep 
the germs from flying into his hair, and pass freely from one 
diphtheria patient to another, inspecting the throat, feeling 
the pulse or smoothing the bedclothes, and occasionally 
stroking his own chin or scratching his head, all without 
washing his hands. And physicians and nurses will continue 
to do such things as long as they fancy that air infection is 
all they have to fear, and forget that there is such a thing as 
contact infection. It has for some years been my custom 
not to wear a gown when called in consultation to cases of 
contagious disease, or when visiting hospital wards, unless I 
am to do much work about the patient. Under the condi- 
tions of a casual visit, even in smallpox, I do not wear a 
gown. It is not necessary to touch anything except with the 
hands, and these should be carefully washed before leaving. 
I have never carried infection to my home, or elsewhere so 
far as known, and I believe that there is no chance of my 
doing so. 

Laundries and Disease. — If clothing can carry infection, 

sickness ought to make its appearance in laundries, to which 

enormous quantities of clothing go even while the infecting 

material is still fresh. Attempts have been made to show 

1 J. Mass. Ass. Bds. of Health, Bost., 1904, XIV, 109. 



IXFECTIOX BY FOMITES 177 

that disease is carried to laundry workers in this way, and 
it is probable that some of the alleged instances are true. 
Thus Sedgwick, and also Walcott, 1 report cases of typhoid 
fever where the evidence was very strong that the disease 
was contracted by handling soiled linen. Thorne-Thorne 2 
also reports an interesting case of probable transmission of 
typhoid fever by clothing. That such accidents are common 
has never been shown. Certainly in Providence there is no 
excess of scarlet fever, diphtheria or typhoid fever among 
laundry workers. This cannot be due to the disinfection of 
the clothing, for much disinfection is not effective, and for 
six years there has been no disinfection after diphtheria, 
and moreover the linen from carriers and missed cases is 
nowhere subjected to disinfection. 

It is true that Landouzy, 3 after examining 1590 laundry 
workers in Paris, states that tuberculosis is twice as prevalent 
among them as among other workers, and he attributes it to 
infection from soiled clothing. But certainly other occu- 
pations show an even greater excess of this disease, and 
there is no suggestion that it is due to infection from the 
materials handled. There may be many other reasons why 
laundry workers should show an excess of tuberculosis, such 
as age distribution, poverty and overwork. 

Infection of Rooms. — It is generally believed that the 
room, or rooms, which have been occupied by a case of con- 
tagious disease are a fertile source of danger to others. The 
germs of diphtheria, scarlet fever and smallpox are sup- 
posed to become attached, not only to books, playthings, 
bedding and furniture, but also to the walls and ceilings. It 
is true that anything which can be reached by the patient 
or attendant may possibly receive infection, the chance in- 
creasing according to the frequency with which the thing is 

1 Sedgwick and Walcott, J. Mass. Ass. Bds. Health, Boston, 1900, 
IX, 145. 

2 Thorne-Thorne, Clin. Soc. Trans., Lond., 1892, XXV, Suppl., 67. 

3 Landouzy, Presse med., Par., 1905, XIII, 633. 



178 THE SOURCES AND MODES OF INFECTION 

handled. That parts of the room or its contents not touched 
should be infected by floating particles, is highly improbable. 
The secretions and excretions which in various ways become 
attached to the contents of the room are usually small in 
amount and thinly smeared on the surface. Such material 
usually rapidly loses its virulence by drying, so that, as is 
shown in these pages, virulent germs are recovered from the 
sick-room in only a small proportion of tests. Nevertheless 
if people should, after the termination of the sickness, crowd 
into the room, rub their moistened fingers over the various 
objects and put the fingers in the mouth, infection might 
sometimes result. But as the germs die rapidly, as probably 
not many persons enter the room, as even visitors would 
usually run little chance of taking up whatever pathogenic 
organisms might be there, we are, I think, justified in assum- 
ing that infection from the room or its contents is not very 
likely to take place. 

" Lung Blocks." — The celebrated " lung block " in New 
York, bounded by Cherry, Catherine, Market and Hamilton 
streets, has had enormous influence on modern views con- 
cerning the transmission of tuberculosis. The great excess 
of tuberculosis in certain tenement houses has given rise to 
a strong belief in its causation by infection which remains 
attached to the interior of the dwelling. We even hear much 
loose talk about the germs of the disease developing in the 
filth and dampness of these dark houses. What an important 
factor house infection is believed to be in the causation of 
this disease is well illustrated by the exceedingly prominent 
place which is given to room disinfection. To judge from the 
attention, time and money bestowed on room disinfection 
after the removal or death of a consumptive, this practice 
is considered of equal importance with hospitals, sanatoriums, 
dispensaries or district nursing as a preventive measure. Let 
us see what is the evidence on which house infection is sup- 
posed to rest. It is apparently that cases continue to occur 
in the same house during successive years. This judgment 



INFECTION BY FOMITES 179 

is based on the spot map. Thus in New York 1 during five 
years, 42 per cent of the deaths from tuberculosis occurred in 
23 of the total houses infected, or in 5.25 per cent of all the 
houses in the city. In Ward IV, 55.8 per cent of the cases 
occurred in 10.5 per cent of the houses in the ward and in 28 
per cent of the infected houses. In Ward VI, 44.7 per cent of 
the cases were in 7 per cent of the total houses and in 19 
per cent of the infected houses. Many in other cities have 
noted the same phenomenon, but it has been especially well 
recorded by the New York Department of Health. But to 
say that these facts are to be largely explained by the per- 
sistence of the tubercle bacilli in the houses is no more rea- 
sonable than it would be to explain the recurrence of an excess 
of murders in certain areas to the persistence of a hypothet- 
ical microbe of homicide. It is true that the advocates of 
the importance of house infection point to numerous in- 
stances in which an apparently healthy family moving into 
a house recently occupied by a consumptive later develop 
the disease. That such should quite often happen merely as 
a coincidence is necessitated by the great prevalence of the 
disease. That in " lung blocks " exposure to living cases in 
the other tenements is a much more likely source of the 
disease than exposure to bacilli on the walls, is probable. To 
demonstrate the relation of the disease to house infection it 
would be necessary to go fully into the history of at least a 
large proportion of the cases, and that, particularly as we 
really know nothing about the latent period of the disease, 
is at present impossible. The excessive incidence of tubercu- 
losis on certain houses is no proof of house infection, and we 
are obliged to appeal to the facts of bacteriology and the 
general principles of infection to estimate the probable dan- 
ger from this source. When we consider the number of per- 
sons who are continually throwing off great numbers of 
tubercle bacilli, and the numberless chances there are, particu- 
larly in the crowded tenement districts, of coming in contact 
1 Rep. Dept. Health, City of New York, 1896, 244. 



180 THE SOURCES AND MODES OF INFECTION 

with fresh infective material, there seems to be no necessity 
of assuming that infection must be traced to the more or less 
feeble and scattered germs that may be clinging to the walls 
of a vacated apartment. What necessity or excuse is there 
for assuming that such infection plays more than an inap- 
preciably minute part in the causation of this disease ? 

Rags and Disease. — Rags have often been considered an 
important vehicle of disease. At one time much attention 
was given to this subject in the United States, and great 
danger was apprehended from the importation of foreign rags, 
and stringent measures were taken to secure their disinfec- 
tion. Lengthy discussions of the matter, and references to a 
great volume of literature, may be found in a report for the 
New York City Board of Health by Smith in 1886, and in the 
Marine Hospital Report for 1893. 1 Numerous references 
are given of the alleged transmission of various diseases by 
means of rags. Among the diseases mentioned are smallpox 
(126 outbreaks), influenza, scarlet fever, erysipelas, typhoid 
fever, septicemia, cholera, and a disease peculiar to rag dust, 
called " flock cough." 

Rags and Smallpox. — It has been believed that small- 
pox is frequently introduced among the workers in paper 
mills by the rags which they handle. Numerous instances 
have been reported from Maine, Massachusetts and Wiscon- 
sin, as well as from foreign countries. Most of the evidence 
is very inconclusive, as no effort is made to exclude other 
sources of infection, and the disease is usually prevailing 
generally at the time. The most suggestive outbreaks are a 
series reported by the Massachusetts State Board of Health. 2 
Here from one to three cases occurred in six mills in different 
localities at a time when there was no smallpox in the town. 
Dr. Abbott, who personally studied these outbreaks, was con- 
vinced that they were due to handling rags. Yet it is curious 
that almost nothing has been heard of this sort of infection 

1 Rep. Surg. Gen. U. S. Mar. Hosp. Serv., 1893, II, 330. 
a Rep. St. Bd. Mass., 1888, xvi. 



INFECTION BY FOMITES 181 

during the last twenty years, and this at a time when small- 
pox was of a remarkably mild type and great quantities of 
clothing worn by patients must have escaped disinfection. 
Abbott was also convinced that, owing to the length of time 
between the collection of the rags and the opening of the 
bales, no danger was to be apprehended from foreign rags. 
Doty 1 says " that the most careful investigation has failed 
to present satisfactory evidence that either foreign or domes- 
tic rags act as a medium of infection." He has personally 
carefully studied the question in Egypt, where many rags are 
collected for the American market, and he says that there is 
no evidence of the infection of the handlers of even the fresh 
rags. 

Rugs and Plague. — Remlinger 2 has recently called atten- 
tion to the supposed danger to be apprehended from draper- 
ies, and particularly also rugs, from the Orient. He rightly 
says that many of the rugs are very filthy, and must have 
been infected during their use or manufacture. Yet during 
all the prevalence of cholera and bubonic plague in Asia dur- 
ing recent years not a single case of these diseases has been 
brought into Europe or America in this way, though great 
quantities of rugs, draperies and rags have been imported 
without disinfection or with very imperfect disinfection. 

Money and Disease. — Money is popularly believed to be 
a common means of spreading disease. Indeed there are few 
things which at first sight seem more likely to do so than paper 
money. Germs readily become attached to its surface, it 
passes rapidly from one person to another, it is kept in inti- 
mate contact with the person, held closely in the hand and 
often put to the lips. Nevertheless there is no good evidence 
that money has ever actually been the means of spreading 
contagious disease. If money is frequently a carrier of infec- 
tion, persons who handle a great deal of money ought to be 
particularly subject to infectious disease. This does not seem 

1 Doty, Med. Rec, N. Y., 1900, LVIII, 681. 

2 Remlinger, Hyg. g6n. et appliq., Par., 1907, II, 257. 



182 THE SOURCES AND MODES OF INFECTION 

to be the case, though there are unfortunately no good pub- 
lished statistics bearing on the subject. However, it is the 
business of the supporters rather than the opponents of the 
theory to produce the figures. I have been on the lookout 
for contagious disease among bank clerks, but the very few- 
cases that have come to my knowledge during the past 
twenty-five years have evidently been contracted in other 
ways. According to Hilditch, 1 the " United States treasurer, 
who has given the subject long and careful consideration, is 
emphatic in his statement that ' there is not the slightest evi- 
dence to show that the employees in his department contract 
infectious diseases any oftener than others who are not in 
this line of work.' " It may be argued, and there is some 
truth in this, that tellers are accustomed to take considerable 
precaution, such as keeping the fingers away from the lips 
and washing the hands before eating. Tram-car conductors 
are, however, I know from observation, particularly prone to 
hold bills and coins between the lips, and are in other ways 
extremely careless, yet they certainly show no excess of scarlet 
fever, diphtheria or smallpox. A bacteriological study of 
paper money has been made by Hilditch above referred to. 
He examined twenty-four bills and found the number of bac- 
teria varied from 14,000 to 586,000 per bill. Pus bacteria 
were found, as was to have been expected, but no other patho- 
genic forms. Hilditch could find accounts of only four other 
similar investigations, none of which, however, were as 
thorough as his. Bacteria are not found in any large num- 
bers on coins, chiefly because of the germicidal action of the 
metal, as shown by the researches of Park, 2 Vincent 3 and 
Bolton. 

Much Evidence Unsatisfactory. — It would be easy to find 
hundreds of alleged instances of fomites infection, in some 
of which the infection was supposed to have persisted for 

i Hilditch, Pop. Sc. Month, N. Y., 1908, LXXIII, 157. 

2 Cited by Hilditch. 

3 Vincent, Abst, Med. News, N. Y., 1892, LXXX, 275 



IXFECTION BY FOMITES 183 

years. Those mentioned in the preceding pages are only a 
few which I happened to have at hand. In most of them 
there is no real evidence that the disease was produced in the 
manner claimed. The error made in claiming so much for 
fomites infection in yellow fever shows how great is the lia- 
bility of error for other diseases. 

Persons, not Things, are Dangerous. — It must also be 
borne in mind that in very many of the reported cases the 
supposed infected articles were carried by some person. That 
the person may be the " carrier" of living germs on his own 
mucous surfaces, though showing no symptoms, we now know 
full well. Until recently this was not known, hence it was 
universal to consider things, not persons, as the bearers of 
infection. We can now see that persons in whom the germs 
are growing are much more likely to be the agents of infec- 
tion than are things on which the germs are dying. Some of 
the instances of alleged fomites infection, such as the room 
infection in scarlet fever referred to, are doubtless really 
instances of carrier infection. 

Fomites and Tetanus. — It is not for a moment to be 
assumed that there are no instances of fomites infection. It 
is not impossible, or at all improbable, that occasionally 
typhoid fever, smallpox, diphtheria and other diseases are 
caused by material things holding the living bacteria for some 
weeks or even for months. In some instances the clinical 
evidence of fomites infection is very strong, though perhaps 
it can rarely if ever be in any individual instance entirely 
conclusive. If it can be substantiated by bacteriological evi- 
dence, it becomes so much the stronger. The strongest evi- 
dence we have of fomites infection is concerning anthrax and 
tetanus. This is not surprising when it is recalled that the 
bacilli of both of these diseases are spore-forming and capable 
in that state of resisting unfavorable conditions of life for 
years. Thus Smith 1 finds that tetanus bacilli will survive 
boiling for sixty minutes at a time, or twenty minutes on 
1 Smith, Theobold, J. Am. M. Ass., Chicago, 1908, L, 929. 



184 THE SOURCES AND MODES OF INFECTION 

each of three successive days. This explains why they have 
been found alive and virulent in commercial gelatine and in 
that situation have been known to give rise to the disease in 
human beings. 1 Of six samples of cotton lamp wick pur- 
chased in various shops in Havana, five were shown by the 
inoculation of white mice to be infected with tetanus. This 
material was used by midwives for tying the umbilical cord, 
and after sterile material was furnished them by the depart- 
ment of health it is said that almost no deaths from infantile 
tetanus occurred in Havana. 2 The number of deaths from 
tetanus in children under one year of age in Havana decreased 
from 128 in 1901 to 18 in 1908. Some of the Fourth of July 
tetanus is believed to be due to the presence of the spores 
in the wads of blank cartridges, and they were demonstrated 
in them by Dolley, 3 and are said to have been found in car- 
tridges in Germany byMusehold of Strassburg and others, but 
several other American observers failed to find tetanus germs 
in a total of 759 cartridges examined. 

Fomites and Anthrax. — The spores of anthrax are so 
resistant that they have been kept for ten or twelve years, 
but the bacilli themselves do not survive any longer than 
typhoid bacilli. Anthrax, though rather rare in the United 
States and England, is very common in some parts of the 
world, particularly in Asia, and the spores are frequently 
imported in dry animal products from Asiatic countries. 
Legge 4 cites from several observers who recovered the spores 
from hair and hides imported from China and Siberia. More 
recently Eurich 5 has examined nearly 750 specimens of wool, 
hair and dust from these materials. In over 600 specimens 

1 Tuck, Jour. Path. & Bacterid., Edinb. & Lond., 1904, IX, 38. 

2 Junta Sup. de San. de la Isla de Cuba, Supplemento y Note Adi- 
cional, 1902-03, 4. 

3 Dolley, J. Am. M. Ass., Chicago, 1905, XLIV, 466. 

4 Legge, Lancet, Lond., 1905, I, 694, and Rep. Insp. of Fact., Lancet, 
Lond., 1904, I, 1206. 

6 Rep. Anthrax Investigation Bd., Bradford, Eng., No. 3, 1908, 8. 



INFECTION BY FOMITES 185 

free from blood he found no anthrax germs, but he did find 
them in 20, or 14.4, per cent, of 139 bloodstained specimens. 
These findings are substantiated in his last report (1909), and 
he speaks of a case of anthrax in a man who handled wool 
in which anthrax spores were actually found. In 64 samples 
of dust, anthrax germs were demonstrated only once. 1 Page 2 
also gives references to other similar findings. But such 
observations are not necessary to show that the disease is 
transported in this way, for there is ample clinical evidence 
that such goods are the direct cause of anthrax in men and 
animals. In fact, most industrial anthrax in Western Europe 
and North America is caused by handling wool, hair and 
hides imported from anthrax-infested countries. 

Fomites and Typhoid Fever. — One of the most remarkable 
of the authenticated instances of fomites infection is the 
transmission of typhoid fever by means of army blankets 
from South Africa. 3 These blankets came from Africa in 
October, 1902, and were then sold. They went to 290 
different parties. One lot used on the transport Cornwall 
apparently gave rise to the disease in May, 1903; the use 
of another lot in England was also followed by typhoid 
fever. Some of the blankets were considerably soiled, and 
living bacilli were found on several that were examined in 
London. 

Fomites and Diphtheria. — A young man working in a 
laboratory in an American city spilled some bouillon culture 
of diphtheria bacilli on his coat. This coat, without disin- 
fection, he wore when calling on the young woman to whom 
he was engaged, and she developed diphtheria two days later. 
The culture which was spilled contained only the branching 
forms of the diphtheria bacillus, and the culture from the 
patient's throat showed the same forms. 

But very few instances other than the above are on record 

1 Rep. of Chief Inspector of Factories and Workshops, 1907, 57. 

2 Page, J. Hyg., Cambridge, 1909, IX, 357. 

3 Parkes, Practitioner, Lond., 1903, LXXI, 297. 



186 THE SOURCES AND MODES OF INFECTION 

where pathogenic bacteria have actually been found on mate- 
rials which presumably have carried infection. According to 
Simpson, 1 plague bacilli were found by Kitasato on cotton 
goods imported into Japan, and this was thought by Kitasato 
to be the way in which the disease was introduced into that 
country, but from what is now known about the mode of 
extension of the disease this seems highly improbable. 

Few Instances of Fomites Infection. — But while we may 
admit that occasionally the virus of even many of the com- 
moner diseases may be retained on fomites for a considerable 
length of time, and ultimately give rise to new cases, there 
is no clinical evidence to show that such instances are at all 
common. Even when carefully sought for, fomites infection 
is not very often found. In my early work as health officer 
I firmly believed in the importance of this factor, and dili- 
gently sought for evidence. The fact that I found very little 
was one thing which led to a more careful consideration of the 
subject. Of 13,970 cases of scarlet fever reported in Michi- 
gan, 2 only 335 were attributed to fomites infection. To an 
even less degree are diphtheria and measles attributed in 
this report to fomites infection. Of 221 cases of bubonic 
plague in Natal, 3 only 8 were by Hill attributed to fomites 
infection, and Mitchell in Port Elizabeth attributed only 
6 of 337 cases to the same source. When we consider that 
most of the evidence is extremely flimsy, and that much of 
the alleged fomites infection is probably carrier infection, and 
remembering also how the history of yellow fever has taught 
us to be wary of such proofs, we are forced to the conclu- 
sion that there is little in the history of the more prevalent 
infectious diseases to indicate that fomites infection is at all 
common. 

Reasons for Belief in Fomites. — One reason why fomites 
infection looms so large in the minds of health officers, as 

1 Simpson, Treatise on Plague, Cambridge, 1905, 204. 

2 Rep. St. Bd. Health, Mich., 1906, 134. 

3 J. Hyg., Cambridge, 1907, VII, 712. 



INFECTION BY FOMITES 187 

well as of the laity, is that the striking character and air 
of mystery about the alleged incidents are so impressive. 
" Death in a Toy," or " A Child Succumbs to the Dread 
Disease from Infection Lurking in its Mother's Shawl," 
appeal to the imagination. That the invisible emanations of 
disease should cling to a garment for years is too near akin 
to the stories of the Arabian Nights not to impress the average 
mind. Hence it is that the comparatively few instances of 
real fomites infection have far more than their due weight 
in our estimation of the relative importance of different modes 
of infection. 

Even if all the alleged instances of fomites infection were 
true,- the amount of disease apparently caused in this way 
is relatively very small. The frequency with which conta- 
gious disease can be traced to fomites is not the reason for 
the general belief in the importance of this mode of infection. 
The real reason, I have no doubt, is, that until very recently 
there seemed to be no other way of explaining isolated cases 
of disease. As a rule it is impossible, even with modern aids 
to the diagnosis of obscure cases, to trace the source of infec- 
tion of most cases of contagious disease, particularly in cities. 
The theory of long persistent fomites infection seemed to 
offer a reasonable solution, and hence met with universal 
acceptance. The theory was almost a necessity to explain 
the facts as they were formerly understood. Now we have 
no need for such a theory, and a much more satisfactory 
explanation is at hand. 

Evidence against Theory. — It is only within a very few 
years that the frequency with which mild atypical cases of 
disease occur has been recognized, and the existence of 
numerous entirely healthy carriers is a modern discovery, 
which is even now denied by some. The more carefully 
individual cases and outbreaks of disease are studied, the 
more often are they traced to missed cases and carriers. 
It is not probable that we shall ever be able to discover the 
origin of all our contagious disease. We can only infer its 



188 THE SOURCES AND MODES OF INFECTION 

source from the data we have. As was shown in the first 
chapter, there is every reason for thinking that disease germs 
rarely grow outside of a living body. Two other theories 
are open to us. Disease may be due to the persistence of 
infection on things, or it may be due to exposure to mild 
cases or carriers. There should be no hesitancy in choosing 
between the danger from rapidly dying germs on books, 
money, furniture or clothes, and rapidly growing germs in the 
mouth, nose and intestines of persons. Moreover things 
must be carried, people move freely at will. 

If the danger from fomites infection were as great as is 
generally believed, the contagious diseases would be much 
more common than they are. The advocates of this theory 
are constantly telling us how easily everything near the sick 
becomes infected and how long the infection lasts. Every 
one knows that at the best disinfection is imperfect, and that 
much that passes for disinfection is no disinfection at all. 
Then the missed cases, which all admit occur in considerable 
numbers, to say nothing of the carriers, are constantly infect- 
ing large numbers of things which are not subjected to any 
disinfection. Yet our scarlet fever and diphtheria are not 
increasing, which means that one case of the disease gives rise 
to no more than another case. If fomites infection occurred 
as easily as is alleged, each case would ramify through 
fomites into a dozen more cases. One reason for doubt about 
the prevailing ideas of fomites infection is this: if fomites 
infection were as common and as easy as is alleged, few 
could escape it, and the infectious diseases would be much 
more prevalent than they are. As was shown in Chapter IV, 
the chances for the transfer of fresh infective material are so 
extremely numerous that there is no necessity for assuming 
the far more difficult and uncertain modes of aerial convection 
and transmission by fomites, and indeed there seems to be 
little opportunity for their action. 

Bacteriological Evidence. — Having considered some of 
the clinical evidence of the part played by fomites in the 



INFECTION BY FOMITES 189 

transmission of infection, it is desirable to inquire what light 
the laboratory study of disease has thrown on the problem. 
One of the first labors of the discoverer of a pathogenic organ- 
ism is to determine its resistance to various hostile influences, 
such as heat, cold, drying, light and disinfectants. 

The Effect of Drying upon Bacteria. — Drying, exposure 
to light and lack of nourishment are the principal factors 
which determine the life of micro-organisms on fomites. 
Besides the study of the germs of special disease by those 
particularly interested, Germano, whose work is mentioned 
in the chapter on aerial infection, Ficker, 1 Zonchello, 2 Heim, 3 
and Buckley, 4 among others, have given careful and system- 
atic attention to the effect of drying on the vitality of bac- 
teria. Exceedingly divergent results have been reported by 
these different observers. This, however, is not surprising if 
the number of factors involved is taken into consideration. 
Among the most important of these factors is the amount 
of light. Germs that are killed in a few minutes in direct 
sunlight may live for weeks in a dark place or even in diffused 
light. The thicker the layer of infectious material, the longer 
is its virulence likely to be maintained. This thickness 
depends largely upon the nature of the medium. In a dried 
watery medium, bacteria may die quickly, while they may 
survive long in sputum or feces. The more complete the 
drying, the shorter the life, and alternate drying and damp- 
ening is unfavorable. The higher the temperature, the 
sooner the germs perish. Their vitality also varies with 
the rapidity of the drying process and the material on 
which they happen to be. Old cultures die sooner than 
fresh ones, and different strains have different powers of 
resistance. The chemical composition of the medium and 

1 Ficker, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1908, LIX, 367. 

2 Zonchello, Giomale della Real Soc. Ital. d' Igiene, 1905, XXVII, 
489, 537. 

1 Heim, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1905, L, 122. 
4 Buckley, Pub. Health, Lond., 1906-07, XIX, 290. 



190 THE SOURCES AND MODES OF INFECTION 

the presence or absence of other organisms may have an 
influence. 

The spores of bacteria are so resistant that we should natu- 
rally expect the diseases caused by the spore-forming kinds 
to be readily carried on fomites. As has been shown, this is 
true of anthrax and tetanus, diseases which belong to this 
class. 

Typhoid Bacilli. — Among the more hardy non-spore- 
forming bacteria is the bacillus of typhoid fever. In the first 
chapter it was shown that in the presence of moisture, as in 
privy vaults, the soil, milk, water, etc., this bacillus some- 
times lives for some months, though it often dies out in a 
much shorter time. It remains to consider the duration of 
its life when in a more or less dry condition. 

Firth and Horrocks 1 found that typhoid bacilli would live 
on khaki for 78 days, in feces dried on serge for 9 to 17 days, 
on serge for 10 days after it had been exposed to direct sun- 
light for 50 hours. Pfuhl 2 says that dried on linen they lived 
97 days. Germano 3 cites Gaffky as reporting that the 
typhoid bacillus would live for 3 months when in a dry con- 
dition, and that UfTelmann recovered it from various dry 
materials after a period of from 21 to 80 days. But Germano 
suspects that the substances were not perfectly dry. Ger- 
mano himself was able to preserve typhoid bacilli dried on 
wood or linen for 90 days, but when he inoculated sterile 
dust with a bouillon culture, the bacilli did not survive over 
4 days and sometimes perished in 1 day. Most of them 
died off very rapidly. Buckley 4 found they would live for 
from 5 days when dried on paper in a room to 119 days 
when kept on wood in a moist chamber. The consensus of 
opinion seems to be that while under unfavorable conditions, 

1 Firth and Horrocks, Brit. M. J., Lond., 1902, II, 936, 1094. 

2 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 

3 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, 
XXIV, 403. 

4 Buckley, Pub. Health, Lond., 1906-07, XIX, 290. 



INFECTION BY FOMITES 191 

as when quite dry and exposed to light, the typhoid bacillus 
may die in a few days, yet under conditions which must fre- 
quently prevail it may remain alive on such things as cloth- 
ing and bedding for some months. 

Mediterranean Fever. — The micrococcus of Mediterra- 
nean fever has about the same resistance as that of typhoid 
fever. Like the typhoid bacillus, it is killed in an hour or 
two in direct sunlight. Dried on glass it survives 16 days, in 
moist soil 72 days and on a blanket 80 days. 1 

Diphtheria. — Loeffler kept dry diphtheria bacilli alive for 
from 9 to 16 weeks, Roux and Yersin for 5 months, D'Espine 
and Morignac for between 3 and 4 months, and Park for 4 
months. 2 Germano 3 found that they would retain their 
virulence after remaining in dry earth or dust for 20 to 40 
days, and Reyes 4 found them virulent in sand and on cloth 
after 14 days. Buckley 5 recovered living bacilli, when dried 
in the air on paper, after 6 days, on wood after 8 days, on 
cotton and on glass after 24 days, and on plaster after 37 
days. Hill 6 exposed to ordinary room conditions, glass rods 
which had been rubbed on a culture of diphtheria bacilli. 
Of these 28 per cent survived 14 days and 9 per cent 20 
days. Houston 7 found that they died very quickly in earth. 
Leighton 8 recovered them from warm moist modeling clay 
up to 18 days. Williams 9 could not recover the germs 
after 24 hours from pencils moistened by the lips of patients 
who had the bacilli in the throat. 

1 Horrocks, Rep. Commission Roy. Soc, Pt. I, 1901. 

2 Cited by Germano. 

3 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, 
XXV, 439. 

4 Reyes, Jahrb. u. d. Fortschr. r . . d. path, mik., Baumgarten, 
1895, XI, 203. 

5 Buckley, Pub. Health, Lond., 1906-07, 290. 

6 Hill, Am. Pub. Health Ass. Rep., 1902, XXVIII, 209. 

7 Houston, Rep. Med. Off. Loc. Gov. Bd., Lond., 1898-99, XXXIII, 413. 

8 Leighton, Pediatrics, 1901, XII, 360. 

9 Williams, N. Y. Health Dept., Sci. Bull. 2, 1895, 16. 



192 THE SOURCES AND MODES OF INFECTION 

Dysentery Bacilli. — According to Pf uhl 1 the bacillus of 
dysentery may remain alive for 17 days when dried on cloth, 
or 10 days when in dry sand. In direct sunlight it dies in 30 
minutes. 2 Kruse 3 claims that when dry it will retain its vital- 
ity for months. 

Tubercle Bacilli. — More attention has been paid to the 
vitality of the tubercle bacillus than to that of other bacteria. 
It is generally believed to be one of the most resistant, but 
Hill 4 has shown that under the same natural conditions of 
dryness, light, etc., the diphtheria bacillus will outlive it. 
Many of the earlier writers claimed a very considerable lon- 
gevity for the tubercle bacilli in dried sputum. Villemin, 
Schill, Fischer, Koch, De Thoma, Sormani, Maffuci and 
Cadeac and Malet claimed a life of from 1 to 9 months. 5 
Ransome and Delepine 6 found that the bacilli if exposed to air 
and light would not survive 45 days, but if kept in dim light 
they did survive. Twichell 7 placed sputum in a folded hand- 
kerchief, in a folded carpet, and spread on wood, and ex- 
posed it to the air at ordinary temperatures and in diffused 
light. The bacilli survived for 39 to 70 days. In sunlight 
they died in a few hours. Migneco 8 found that when dried 
on cloth in the sun they lived from 20 to 30 hours. 

Not so Resistant as Believed. — Many recent observers 
do not find this bacillus so resistant as has been supposed. 
That it perishes in direct sunlight in less than an hour seems 
certain. Weinzirl, 9 using improved methods, finds that it 
will not survive 10 minutes, and frequently dies in 2 minutes. 

1 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 

2 Shiga, Deutsche med. Wchnschr., 1901, XXVII, 765, 783. 

3 Kruse, Deutsche med. Wchnschr., 1901, XXVII, 370, 386. 
* Hill, Am. Pub. Health Ass. Rep., 1902, XXVII, 209. 

5 Kolle and Wasserman's Handbuch [etc.], Jena, 1903, II, 108. 

6 Ransome and Delepine, Proceedings Royal Society, No. 336. 

7 Twichell, Med. News, N. Y., 1905, LXXXVII, 642. 

8 Migneco, Arch, of Hyg., Miinchen u. Leipz., 1895, XXV, 361. 

9 Weinzirl, J. Infect. Dis., Chicago, 1907 [Suppl. No. 3], 128. 



INFECTION BY FOMITES 193 

Cadeac * spread sputum on marble and could find no living 
germs after the fourteenth day. On a porous plaster plate 
they died within 2 days. Hill 2 dried sputum on glass rods 
in the air under ordinary room conditions, and found no liv- 
ing bacilli at the time of his first test, which was made after 
16 days. Rickards, Slack and Arms 3 have made very careful 
tests by exposing sputum on wood and cloth in the rooms of 
ordinary tenements. They find that when dry and kept in 
diffused light the bacilli will live about 1 month, in dark and 
dry rooms up to 85 days; another strain survived only 45 
days under the latter conditions. Rosenau 4 sa3 r s that further 
work upon the viability of the dried tubercle bacillus may 
change our views as to its hardiness, and failure to recognize 
lesions produced by the dead bacillus is responsible for some 
of the false conclusions reached by certain experimenters. 

Plague Bacilli. — Simpson 5 states that the German Plague 
Commission found that in a large number of experiments with 
sputum, blood, etc., dried on all sorts of materials, under 
natural conditions, the bacilli of bubonic plague do not sur- 
vive over 8 days. Of many specimens of the organism dried 
on cover glasses and sent to England, none survived the 
journey. Kitasato 6 found that plague pus dried on cover 
glasses lost its virulence, when exposed to the sun, in from 
3 to 4 hours, and this has been substantiated by others. As 
was referred to in the first chapter, the work of the last Eng- 
lish Plague Commission shows that virulent plague bacilli 
cannot be found in the dirt floors of native houses after 48 
hours. According to the careful experiments of Buckley, 7 

1 Cadeac, Lyon med., 1905, CV, 865, Abst. Brit. M. J., Lond., 
1906, I. 

2 Hill, Am. Pub. Health Ass. Rep., 1902, XXVIII, 209. 

3 Rickards, Slack and Arms, Am. J. Pub. Hyg., Bost., 1909, V, 586. 
* Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. 

No. 57, 1909. 

5 Simpson, Treatise on Plague, Cambridge, 1905, 96. 

8 Kitasato, Lancet, Lond., 1894, II, 428. 

7 Buckley, Pub. Health, Lond., 1906-07, XIX, 290. 



194 THE SOURCES AND MODES OF INFECTION 

plague bacilli remain alive after drying in the air, for 11 hours 
when dried on cotton, 2 hours on wood, 5 hours on plaster, 
2 hours on glass, and 3 hours on paper. When kept in a 
desiccator they survived on cotton for 22 hours, and in a 
moist chamber for only 36 hours. Gotschlich, 1 by folding 
material containing the germs in cloth, could preserve them 
alive for from 3 to 4 weeks. Simpson 2 reports that infected 
cloth may retain its virulence for 80 days. According to 
Verjbitski, 3 the crushed viscera of experimental animals and 
the crushed bodies of fleas when smeared on cloth and dried 
will preserve the bacilli alive for 130 days at a temperature 
of 4-5° C, and for 35 days at room temperature. Bandi and 
Stagnitta-Balistreri state that these bacilli may survive in the 
bodies of dead rats for 2 months. The vitality of the plague 
bacillus has been carefully investigated by Rosenau, 4 who 
does not consider it a frail organism. Temperature is the 
most important factor in its life. It may lose its virulence 
before it loses its vegetability. It dies in a few days on the 
dry surface of hard objects and on paper. Rosenau says that 
bedding may harbor the infection for a long time. Tidswell, 5 
experimenting with a large number of materials, found that 
plague bacilli dried under natural conditions lived only 
from 3 to 4 days, but when dried slowly on muslin they 
might live for 21 days. The colder the climate the greater 
is the chance of the persistence of infection. In this all are 
agreed. 

Pus-forming Bacteria. — The pus-forming bacteria are quite 
resistant to drying. According to Germano, 6 streptococcus 

1 Gotschlich, cited by Kolle and Wasserman's Handbuch [etc.], 
Jena, 1903, II, 496. 

2 Simpson, Treatise on Plague, Cambridge, 1905, 93. 

3 Verjbitski, J. Hyg., Cambridge, 1908, 203. 

4 Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. 
No. 4, 1901. 

5 Tidswell, Report on Plague in Sydney, J. A. Thompson, 1902, 67. 

6 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXVI, 
66. 



INFECTION BY FOMITES 195 

withstands drying for a month, but different strains have 
varying degrees of resistance. See also Heim 1 and Neisser, 2 
who found that these organisms would withstand drying for 
a long time. Buckley 3 could keep staphylococcus alive for 
only 7 days when on paper in the air, and on other sub- 
stances and under different conditions for varying times, up 
to 130 days on cotton kept in a desiccator. 

Cholera Spirilla. — Germano 4 in a number of experiments 
found that the cholera spirillum in dried feces lived only 3 
days and in other experiments only 1 day. He also cites Zon- 
chello as reporting that it is among the least resistant bac- 
teria. Kitasato 5 states that it may retain its virulence up 
to 8 days, but that it may die sooner, especially when dried on 
glass. Usually it lives from a few hours up to 4 days. Koch 
and GafTky 6 state that when dried on glass it survives only 
a few hours, but when dried on fabrics it may retain its viru-» 
lence up to 4 days. Buckley 3 found that cholera germs would 
survive when dried in the air, 9 hours on. cotton, 8 hours on 
wood, 11 hours on glass, and 5 hours on paper. They did 
not survive nearly so long when dried in a desiccator. This 
is contrary to the experience of others, for as a rule bacteria 
live much longer when dried in a desiccator than when dried 
in the open air under natural conditions. Gotschlich 7 says 
that cholera germs will live in dejecta dried in the air on 
clothing for 36 days, and when damp, according to Karl- 
niski's observations, for 7 months. He considers that such a 
long life is exceptional, and that generally the spirillum dies 
in a few days. A duration of only a few days, or even hours, 

1 Heim, Ztsch. f. Hyg. u. Infectionskrankh., Leipz., 1905, L, 122. 

2 Neisser, Ueber Luftstaub-Infection, Inaug. Dis., Breslau, 1898. 

3 Buckley, Pub. Health, Lond., 1896-97, XIX, 290. 

4 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, 
XXIV, 403. 

5 Kitasato, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1885, V, 134. 

6 Koch, Arb. a. d. k. Gesundsamte, Berl., 1886, I, 199. 

7 Gotschlich, Kolle and Wasserman's Handbuch [etc.], Jena, 1902, 
I, 211. 



196 THE SOURCES AND MODES OF INFECTION 

was also found by Gamaleia, 1 Hesse 2 and Koch and 
Gaffky. 

Pneumococci. — The pneumococcus is widely distributed 
in healthy human mouths, and the opportunities for the 
direct transference of fresh secretion are so numerous that 
it probably is of no importance whether this organism lives 
long or not. Wood 3 found that while pulverized sputum lost 
its virulence in a few hours when dried in mass, it might, 
under favorable conditions, retain it 35 days. Buerger 4 recov- 
ered the pneumococci from a handkerchief 7 days after it had 
been in use. Germano 5 and some others claim a consider- 
ably greater resistance. Germano kept it alive in dust for 
140 days, but the tendency of later observers is to consider 
it a much feebler organism. 

Influenza Bacilli. — According to Pfeiffer, 6 the influenza 
bacillus retains its vitality when dried in sputum for 36 to 40 
hours. When dried on a cover glass and kept at 37° C., it 
survives for only 2 hours, and when kept at room temperature 
for from 8 to 20 hours. 

Meningococci. — The evidence in regard to the germ of 
cerebro-spinal meningitis appears to be somewhat conflicting. 
Germano and Neisser claim considerable resistance for it, as 
also does Jaeger. 7 Germano said it would live for 80 to 90 
days, but it is said that he did not work with the true menin- 
gococcus. 8 More careful and recent observers do not find it 
so resistant. Councilman 9 found that it would live when dry 

1 Gamaleia, Deutsche med. Wchnschr., 1893, XIX, 1350. 

2 Hesse, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1893, XIV, 30. 

3 Wood, J. Exper. M., N. Y., 1905, VII, 592. 

4 Buerger, J. Exper. M., N. Y., 1905, VII, 518. 

5 Germano, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., 1897, XXVI, 66. 

6 Pfeiffer, Nothnagel's Encycl. Pract. Med., Phila. and Lond., Influ- 
enza, 1895, 584. 

7 Jaeger, Med. Klin., Berl., 1905, I, 990, 1011. 

8 Arkwright, J. Hyg., Cambridge, 1907, VII, 193. 

9 Special Report on Cerebro-spinal Meningitis, Mass. St. Bd. 
Health, 1898, 78. 



INFECTION BY FOMITES 197 

in a dark room less than 72 hours. Albrecht and Ghon 1 
could keep it only 24 hours in the dark, and Bettencourt and 
Franca 2 less than 9 hours. Kache, 3 Kutscher 4 and Fliigge 
had similar results, and Arkwright 6 succeeded in keeping the 
organism alive only from 20 to 48 hours. Lingelsheim 7 says 
that in culture media it dies in a few hours, but in sputum 
it may be kept alive for 5 days. 

Gonococci. — Among the least resistant bacteria is the 
gonococcus. According to Schaffer and Steinschneider, 8 it 
lives only a few hours when dried, and frequently dies as 
soon as thoroughly dry. Gonorrheal pus dried on a 
towel lost its virulence in 36 hours, and dried on linen it 
lived only a few hours. 9 I have been unable to find any 
experimental evidence as to the resistance of the spirochete 
of syphilis. 

Bacteria on Fomites. — Pathogenic bacteria have fre- 
quently been sought for on various articles believed to be 
likely to be the means of transporting disease, but with the 
exception of the spores of anthrax and tetanus they have 
rarely been found. The finding of anthrax and tetanus spores 
has already been referred to. Besides the places mentioned, 
tetanus germs have been found in the soil in various places, 
in the dirt filling between the floors of houses 10 and in one 

1 Albrecht and Ghon, Wien. klin. Wchnschr., 1901, XIV, 984. 

2 Bettencourt and Franca, Ztsch. f. Hyg. u. Infectionskrankh., Leipz., 
1904, XLVI, 463. 

3 Cited by Flugge. 

4 Kutscher, Deutsche med. Wchnschr., 1906, XXXII, 1071. 

5 Flugge, Klin. Jahrb., Jena, 1905, XV, 373. 

6 Arkwright, J. Hyg., Cambridge, 1907, VII, 193. 

7 Lingelsheim, Klin. Jahrb., Jena, 1905, XV, 373; Ztschr. f. Hyg. u. 
Infectionskrankh., Leipz., 1908, LIX, 457. 

8 Verhandl. d. IV Kong. d. deutsch. dermatol. Gesellsch., Breslau, 
1904. 

9 Ullmann, Wien. med. Blatter, 1897, XX, 703 et seq. 

10 Heinzelmann, Miinchen med. Wchnschr., 1891, XXXVIII, 185, 
200. 



198 THE SOURCES AND MODES OF INFECTION 

instance in a house where there had been a death from 
tetanus. 1 

Distribution of Germs of Suppuration. — The pus organ- 
isms are quite resistant to drying, and if they were not, they 
are so widely distributed, being found constantly on the skin 
and mucous surfaces of human beings, that their presence 
might be expected wherever human beings are found. They 
have as a matter of fact been found almost wherever sought, 
as on clothing, books, money, instruments, floors and wood- 
work, and indeed on anything that is touched by the hand 
of man. 

Diphtheria Bacilli on Fomites. — Diphtheria bacilli have 
been frequently searched for on all kinds of objects and fre- 
quently found. Abel 2 and Wesbrook 3 found them on toys, 
and in Abel's case it was 86 days after infection. Trevelyan 4 
recovered them from a handkerchief 11 weeks after it had been 
used by a diphtheria patient. Park 5 took cultures which 
proved positive in almost every instance, from dried stains on 
bedclothing soiled by children sick with diphtheria. He also 
found the bacilli alive in a piece of membrane after 4 months. 
Wright and Emerson 6 made 20 cultures from various articles 
in the Boston City Hospital, and found 5 positive. Of these 
3 were from the shoes, 1 from the hair of an attendant, and 

1 from a floor brush. Schumburg 7 in 40 cultures from a 
room occupied by a diphtheria patient recovered virulent 
bacilli from a drinking glass and the handle of a mirror. In 

2 of the 5 cultures the virulence of the organism was low. 

1 Gotschlich, Kolle u. Wasserman's Handbuch [etc.], Jena, 1902, 1, 210. 

2 Abel, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1892, XIV, 
756. 

3 Wesbrook, Wilson and McDaniel, Am. Pub. Health Ass. Rep., 
1899, XXV, 546. 

4 Trevelyan, Lancet, Lond., 1900, I, 1443. 

5 Park, Med. Rec, N. Y., 1892, XLII, 116. 

6 Wright and Emerson, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., 
Jena, 1894, XVI, 412. 

7 Schumburg, Ztschr. f. arztl. Fortbild., Jena, 1905, II, 567. 



IXFECTIOX BY FOMITES 199 

Weichardt 1 took 300 swabbings from various things in a 
sick-room and 250 from other parts of the house, and found 
diphtheria germs 3 times on objects which had been in contact 
with the patient's mouth. Hill 2 took 532 swabbings from a 
room occupied by a diphtheria patient, and obtained 4 posi- 
tive results, all of which were from objects handled by the 
patient. In Providence about 200 swabbings taken under 
similar circumstances showed no diphtheria bacilli. These 
last three observations indicate that diphtheria bacilli are 
not very numerous, even on objects brought into close con- 
tact with the patient. Kober 3 could find no bacilli on the 
floor, bed linen, etc., of 10 houses in which there had been 
diphtheria, and he states that Heymann did not find them 
in the Hygienic Institute at Breslau. Klein could not find 
them on telephones in London, 4 and Hill in Boston 5 could 
not find them on 24 mouthpieces of lung-testing machines. 

Tubercle Bacilli on Fomites. — While the tubercle bacillus 
is not so resistant to drying as was formerly thought, it is 
discharged in such numbers in the sputum that it has been 
found outside of the body more often than have any other 
organisms except the pus-forming bacteria. Reference to 
finding it in dust will be given in the next chapter. When 
in considerable masses of sputum, and kept damp, the bacillus 
will survive longer than when mixed with dust. Besides on the 
floors and various articles in rooms, the bacillus has been 
found in books which were in use for some years in a circu- 
lating library. 6 Petersson 7 examined the history charts kept 
by the bedside of tuberculous patients and put away for 

1 Weichardt, Jahresb. u. d. Fortschr. . . . d. path. Mik., Baum- 
garten, 1900, XVI, 197. 

2 Hill, Am Pub. Health Ass. Rep., 1902, XXVIII, 209. 

3 Kober, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXXI, 449. 

4 Klein, Abet. J. Am. M. Ass., Chicago, 1905, XLIV, 1866. 

5 Hill, Rep. Bd. Health, Boston, 1906, 91. 

Mitulescu, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1903, 
XLIV, 397. 

7 Petersson, Ztschr. f. klin. Med., Berl., 1907, LXIII, 346. 



200 THE SOURCES AND MODES OF INFECTION 

periods varying from months to years. He found by micro- 
scopic examination tubercle bacilli on two books that were 
kept for six years. Bissell 1 washed the pockets of some uni- 
forms that had been used by soldiers sick with consumption, 
and obtained two positive results by guinea-pig inoculation. 
Friberger 2 used a vacuum cleaner to remove the dirt from 
clothing fresh from use by tuberculous patients, and found 
virulent bacilli in 3 of 12 tests. 

Cholera Spirilla. — Although the life of the cholera spiril- 
lum outside of the body appears to be short, usually only a 
few days and often less, some early observers, as Babes, 3 claim 
to have found it on the personal effects of cholera patients. 

Resistance of Protozoa. — There is no theoretical reason 
why the protozoan blood parasites might not, in a spore-like, 
resistant stage, withstand drying and remain alive for some 
time outside of the body. But there is no experimental evi- 
dence to show that in any of the well-known protozoan dis- 
eases such spores are formed. There is certainly no clinical 
evidence to show that such diseases are ever carried on 
fomites, and for malaria, yellow fever, sleeping sickness and 
Texas cattle fever there is convincing evidence that they 
are not so carried. 

Resistance of Vaccine Virus. — With two exceptions, prac- 
tically no experimental work has been done with the virus 
of any of the infectious diseases, a specific organism for which 
has not been determined. Vaccine virus has an extensive 
use, and it is desirable to store it and transport it long dis- 
tances, so that its keeping qualities have received considerable 
attention. When the infectious material dries naturally in 
the crust which forms from the vesicle, it retains its virulence 
for a considerable time. These crusts were largely used in 

1 Bissell, Med. News, N. Y., 1899, LXXIV, 156. 

2 Friberger, Ztschr. f . Tuberk. u. Heilstaltenw., Leipz., 1908-09, XIII, 
37. 

3 Shakespeare, Report on Cholera in Europe and India, U. S. Gov. 
Print. Off., 1890, 606. 



INFECTION BY FOMITES 201 

Providence for maintaining the Jennerian strain of vaccine, 
which was used in the health department for nearly fifty 
years. The crusts, when taken from the arm and kept 
wrapped in paper in a dark place, could be relied upon to 
retain their virulence for a month, and often did retain it 
longer. When kept in a tightly corked bottle in a refrigerator, 
they will generally remain virulent over 6 months. If exposed 
to light and air and varying temperature, the virulence may 
be lost in less than a month. A thin layer of the same lymph 
on a quill does not remain active when exposed to the air 
for more than a week or ten days. The ivory points covered 
with vaccine matter, which were so much used a few years 
ago, were usually guaranteed to keep 3 weeks, and often did 
remain virulent a month or more. But there was usually 
more than one layer, and the thickness of the material was 
further increased by the presence of blood and leucocytes. 
According to Seaton, 1 dried vaccine matter on points may 
keep for from 6 or 9 months or more, and he quotes Husband 
as securing successful vaccinations from 7 of 93 dried points 
kept for periods varying from 6 to 30 months. Vaccine matter 
in powder also has been kept by Warlomont and others for 
several months. 2 Recently Green 3 has kept dried pulverized 
vaccine matter in sealed tubes for periods varying from 20 
days at 37° C. to 252 days at 10-15° C. and 301 days at 
4° C. Although under exceptional circumstances dried vac- 
cine matter may be kept a considerable time, it requires great 
care and often results in failure. Hence early in the nine- 
teenth century, in order to introduce vaccination into her 
American possessions, the Spanish Government 4 sent out a 
ship with a number of children on board, so that by successive 
arm-to-arm vaccinations fresh lymph might be carried across 
the seas. At the end of the nineteenth century, when Porto 

1 Seaton, Handbook of Vaccination, 1868, 172. 

1 Warlomont, Manual of Animal Vaccination, Phila., 1886, 139. 

" Green, J. Hyg., Cambridge, 1908, VIII, 528. 

4 Life of Jenner, Baron, I, 606; II, 78. 



202 THE SOURCES AND MODES OF INFECTION 

Rico came under the control of the United States, the diffi- 
culty of transporting vaccine virus to the island became so 
great, so little active virus surviving even this short voyage, 
that it was necessary to establish a vaccine farm on the island. 
In the Philippine Islands it was found to be necessary to 
transport the virus packed in ice to inland villages. 1 

Resistance of Smallpox Virus. — It is a common belief that 
the crusts in variola are infectious, and they are supposed to 
have been used at times in the practice of inoculation. I do 
not remember to have seen any evidence of this till I came 
across the work of Brinckerhoff. 2 He refers to a rather limited 
literature, and details his own experiments, which determined 
a persistence of virulence in the crusts for periods of from 22 
to 52 days, and in one instance to 88 days. 

Comparative Resistance. — Experiment shows that some 
pathogenic organisms, like those of gonorrhea and cerebro- 
spinal meningitis, are of such feeble resistance that infection 
by fomites, as ordinarily understood, is in these diseases highly 
improbable. It is also shown that certain other bacteria, as 
those of diphtheria, typhoid fever and tuberculosis, are resist- 
ant enough to make infection by fomites very possible. But 
it appears that all known pathogens, except those having 
spores, tend to die off quite rapidly outside of the body, and 
that under natural conditions it is rather the exception for 
them to persist for any great length of time. It is worth 
noting that the typhoid bacillus is more resistant than any 
other pathogenic organism referred to. Yet we hear almost 
nothing about fomites infection in that disease. Is it not 
because attention has been directed to other sources which 
have been believed to be sufficient, so that there has been 
little temptation to assume infection by fomites ? Infection 
by fomites has, on the other hand, been considered of much 
importance in cholera, the spirillum of which is far less resist- 
ant than is the bacillus of typhoid fever, probably because 

1 Rep. Bd. Health, Philippine Isl., 1904-05, 23. 

2 Brinckerhoff, J, Med. Research, feost., 1904, XI, 284. 



INFECTION BY FOMITES 203 

in the absence of the knowledge of carriers which we now 
possess the world-wide diffusion of this disease seemed inex- 
plicable except by means of fomites. 

Experiments with Yellow Fever. — With a few notable 
exceptions, little experimental work has been done to deter- 
mine the part played by fomites in the spread of disease. 
When Reed, Carroll Lazear and Agramonte proved that yel- 
low fever is transmitted by the mosquito, it still remained 
uncertain whether it might not also be carried in other ways, 
and sanitary officials were generally so convinced of the over- 
whelming evidence of the great part played by fomites, that 
definite proof or disproof of the fact was earnestly desired. 
The complete failure of the commission to produce the disease 
in human beings by fomites is well known, and their experi- 
mental work has now been corroborated by abundant clinical 
evidence from all the great endemic foci of this disease. In 
these experiments, non-immunes were confined in a small 
room for a number of days in close contact with bedding and 
clothing fresh from yellow-fever cases, most of which was 
soiled with excreta and vomitus. 1 The experiments were 
repeated a number of times, but in no instance did the disease 
develop. When not long after I stood in one of those dirty 
little rooms in company with Dr. Finlay and Dr. Gorgas, and 
saw some of the old bedding lying in the corner, I realized 
as never before how very much greater are the difficulties in 
observation than in experiment, and it seemed that the time 
had come when the prevailing views as to the importance of 
fomites infection in other diseases than yellow fever should 
be seriously reviewed. 

Observations on Plague. — In another disease, bubonic 
plague, exceptionally brilliant work, from the purely epidemi- 
ological standpoint, has been done by Thompson in Australia. 
It is true enough that conditions are much more favorable for 
observation when a disease first invades a country than when 
it has become as widespread as plague is in India, but in no 
1 Phila. M. J., 1900, VI, 790. 



204 THE SOURCES AND MODES OF INFECTION 

place have they been taken advantage of as they were in 
Sydney. Thompson 1 showed conclusively that rat plague 
preceded human plague, that the flea was the intermediary 
between rat and man, and that in New South Wales, at least, 
fomites had no part in the diffusion of the disease. These 
observations have been confirmed in other parts of Australia. 2 
Experiments with Plague. — The present English Plague 
Commission have, by their ingenious and painstaking ex- 
periments and observations in India, confirmed Thompson's 
work. Reference will be made in another chapter to the 
experiments on the transmission of the disease by the air, in 
which they definitely proved that aerial infection does not 
take place. They also studied experimentally the conditions 
of house infection, and their work is among the best planned 
and executed and the most convincing of any that has ever 
been attempted for any disease. Besides much other work, 
they placed guinea pigs in the houses of an Indian village 
just vacated by the inhabitants because of plague, thus sub- 
stituting an experimental population under control for the 
normal human population. 3 The results were in every way 
in accord with the view that plague is primarily a rat disease, 
and is transmitted from rats to man, or to other animals, by 
means of fleas. In these and in similar less extensive experi- 
ments 4 there was evidence to show that the animals could 
not contract the disease from the dwellings themselves. • To 
test more definitely the possibility of transmission by fomites 
other experiments were made. The floors of houses were 
soaked with cultures of the bacilli, and guinea pigs placed 
upon them. Of 24 exposed during the first hour after in- 
fection 4 died; of 12 exposed up to six hours 4 died; but 
during all this interval pools of the culture were upon the 
floor. Of 24 animals exposed after twelve hours only 1 

1 Thompson, J. Hyg., Cambridge, 1906, VI, 537. 

2 Ham, Rep. on Plague in Queensland, 1900-07, Brisbane, 1907. 

3 J. Hyg., Cambridge, 1907, VII, 799-875. 

4 J. Hyg., Cambridge, 1906, VI, 450-482. 



INFECTION BY FOMITES 205 

succumbed. Guinea pigs were also allowed to run freely 
about hospital wards in which cases of bubonic plague were 
being treated, and 15 were confined in a room with freshly 
soiled bedding, which was renewed every day for six weeks. 
In none of the animals did the disease develop. Again (p. 
887), clothing from infected houses, removed without precau- 
tions to prevent the transport of fleas, was placed in cages 
containing 26 guinea pigs, 1 of which died of the plague. A 
few fleas which had been brought in the clothing were found in 
the cages. It seems to be quite clear from these experiments 
that while infection by fomites is possible, it is probable only 
when the infection is exceedingly gross and the contact is inti- 
mate, as in the case of the infected floors referred to above; or 
it may also be possible when infected fleas are transported in 
the goods. How common this is has not yet been determined. 

Tuberculosis. — I know of no other diseases in which seri- 
ous experimental work has been done to determine the part 
played by fomites in their diffusion. It is particularly remark- 
able that tuberculosis has not been thus critically studied. 
Every one has been calling for room disinfection as a powerful 
means of combating this disease, yet it does not seem to have 
occurred to any one to place susceptible animals in a series of 
supposedly infected rooms (as was done in the case of plague 
in India) to determine if possible how great the danger from 
room infection really is. 

Disinfection of Little Value. — From a consideration of the 
facts presented in this chapter the writer became convinced 
some time since that the danger from fomites infection is 
for most diseases very much less than is generally believed. 
In diphtheria particularly it appeared that little if any sick- 
ness could be due to infection remaining about the house or 
its contents after the termination of isolation. As isolation 
is almost invariably terminated without any reference to the 
presence of carriers in the family, it appeared to be absurd 
to disinfect the material things in the house when in all prob- 
ability some carrier was still growing the bacilli. Hence in 



206 THE SOURCES AND MODES OF INFECTION 



March , 1905, terminal disinfection was abandoned in Provi- 
dence, except in those very few instances in which the family 
was willing to wait for two successive negative throat and 
nose cultures from each of its members. The attempt was 
thus made to test the importance of fomites infection by 
abandoning disinfection and noting any change that might 
occur in the prevalence or distribution of the disease. One 
obvious way of testing the influence of disinfection is to com- 
pare the recurrence of the disease after disinfection with the 
amount which occurred after the warning placard was re- 
moved without disinfection. The following shows the recur- 
rences in the two classes of cases. 

The number of recurrences after disinfection, the number 
of infected families and the ratio between the two, during 
the years 1902 and 1905, was as follows: 



Year. 


Infected 
Families. 


Recurrences. 


Ratio. 


1902 

1903 

1904 

1905 


358 
453 
559 

87 
1457 


6 

7 
10 

2 

25 


1.67 
1.54 

1.78 
2.30 
1.71 


Total 



The number of recurrences since February, 1905, where 
there was no disinfection and the ratio to infected families 
where there was no disinfection are as follows: 



Year. 


Infected 
Families. 


Recurrences. 


Ratio. 


1905 


258 
259 
343 
687 
472 
2019 


4 

4 

7 

17 

10 

42 


1.55 
1.55 
2.04 
2.34 
2.12 
2.08 


1906 


1907 

1908 


1909 


Total 



INFECTION BY FOMITES 207 

The period from 1902 only is taken, because previous to that 
time the duration of isolation was somewhat longer, but there 
has been no change since. Very few health officers keep any 
record of the recurrences in diphtheria and other infectious 
diseases, but it is interesting to note that in Baltimore, where 
terminal disinfection is practiced in an unusually thorough 
manner, and is in a large majority of cases tested for its effi- 
ciency, recurrences in diphtheria occur in 1 .89 per cent of the 
cases. 

Again, it may be objected that recurrence in the family is 
no criterion of the infection of the house, for it may be that 
the family is largely immune. This would certainly be much 
less true of those members of the family who went away dur- 
ing the sickness. Of 510 minors who thus returned to the non- 
disinfected house only 1 was taken sick. So too if terminal 
disinfection is such an important matter, its neglect should be 
followed by an increase in the disease. As a matter of fact, 
after disinfection was abolished diphtheria diminished, until 
at one time in the following August there was not a single 
reported case in the city. Again in August, 1908, the disease 
was reduced to a single recognized case. There has been a 
marked increase since, common to many parts of New Eng- 
land, and the excess in Boston, where disinfection is practiced, 
has been greater than in Providence. Still another test of the 
danger from the omission of disinfection is the extension of 
the disease to other families in the same house. Of over 1200 
such families only 10 were invaded by the disease within two 
months after the termination of isolation in the non-disin- 
fected apartment. It may be suggested that though no offi- 
cial disinfection was practiced, the houses were perhaps 
thoroughly cleansed by the occupants. I must confess that 
I hoped that the abandonment of official disinfection would 
cause people to do more cleansing for themselves, but there 
has thus far been little improvement, and as a large part of 
our diphtheria occurs among poor and ignorant people, many 
of whom are recent immigrants, house cleaning by the family 



208 THE SOURCES AND MODES OF INFECTION 

can scarcely be expected to be very efficient at present. It 
appears, then, that this experiment shows that house infection 
in diphtheria is in Providence a negligible factor in the dis- 
semination of the disease. 

French Views on Disinfection. — Recently, 1 at a discussion 
in Paris, Comby, Courmont and Lemoine took the ground 
that the active disinfection which has been insisted on in that 
city in recent years has not reduced the mortality from scarlet 
fever, diphtheria or measles, for which diseases it is required. 
Comby 2 is emphatic in his contention that it is persons, not 
things, that are the bearers of contagion. The same position 
was taken by Semaine Medicate for February 14, 1906. 
Lemoine 3 has found disinfection not so essential as has been 
claimed. At the hospital at Val de Grace certain rooms were 
used for isolating single cases of contagious disease. There 
was often such demand for their use that cases of different 
diseases quickly succeeded one another, sometimes without 
any disinfection and often with slight disinfection by washing 
the walls as high as could be reached. Sixty-five cases of 
scarlet fever, 41 of measles, 25 of mumps, 31 of diphtheria, 
4 of smallpox, 1 of chicken pox and 136 of other diseases are 
reported as rapidly succeeding one another in these rooms. 
One case of measles and 4 of scarlet fever developed in the 
rooms. Often it was necessary to shift entire wards of twenty 
to thirty beds, with only a slight attempt at disinfection. This 
was done a good many times during nine years without bad 
results. 

When official disinfection after measles was temporarily 
suspended in New York from January 10, 1908, to March 1, 
neither the suspension nor the resumption of the practice 
appeared to have any effect on the epidemic curve. Rich- 
ards 4 does not consider disinfection of the room necessary, 

1 Bull, et mem. Soc. meU d. hop. de Par., 1909, n. s., XXVII, 585. 

2 Comby, Presse med., Paris, 1909, XXVII, 249. 

3 Lemoine, Rev. d'hyg., 1907, XXIX, 1057. 

4 Richards, Pub. Health, Lond., 1909, XXIII, 42. 



INFECTION BY FOMITES 209 

provided the floors are washed and things which come in 
contact with the patient are cleansed and disinfected. 

School Disinfection. — When a number of cases of scarlet 
fever or diphtheria develop in a school, the public is inclined 
to consider room infection the source and to demand " dis- 
infection." This subject has lately, perhaps owing in part 
to the efforts of sellers of disinfectants, been much discussed 
in England, but fortunately the leading officials refuse to be 
influenced by public clamor. Among others, Kerr 1 has clearly 
set forth the reasons why the room can rarely be at fault in 
school outbreaks of the contagious diseases. 

Disinfection Unnecessary in Other Diseases. — Owing to the 
similarity between the two diseases it seems to me that there 
is probably no more value in disinfection after scarlet fever 
than there is in disinfection after diphtheria. In fact in any 
disease which is widely distributed, and in which there is ample 
opportunity for extension from mild cases, from carriers, from 
cases in the early stages, and from convalescents, the absolute 
disinfection of all possible fomites at the assumed termina- 
tion of the sickness will probably have no influence in check- 
ing the disease. Thus I can see no use in disinfecting after 
measles, whooping cough, influenza, pneumonia or cerebro- 
spinal meningitis, and I think that this view is held by the 
majority of our health officers and epidemiologists. Disin- 
fection after diphtheria is absurd unless it be shown by two 
or three negative cultures that none of the family are still 
growing the bacilli. Disinfection after cerebro-spinal menin- 
gitis is also absurd, as the meningococcus lives only a few 
hours, and carriers are almost the sole means by which this 
disease is spread. Much disinfection after tuberculosis is also 
without reason. If a patient has been living with his family 
and taking no precautions, certainly no amount of terminal 
disinfection will atone for long-continued sanitary sin. If 
precautions are taken, the phthisiologists tell us that there 
is no danger in living with the patient, and if so, certainly 
1 Kerr, Pub. Health, Lond., 1909, XXIII, 49. 



210 THE SOURCES AND MODES OF INFECTION 

there can be no possible danger in living in his house after 
he is dead. The only occasion for disinfection after consump- 
tion, then, is when the apartments of a careless patient are to 
be occupied by another family, and, after all, we have no evi- 
dence to show how much danger there is even then. Yet 
many health officers make disinfection after every death from 
consumption the first and often the only measure taken to 
restrict tuberculosis. 

When Terminal Disinfection is Desirable. — When a new 
or rare disease invades a locality, it may at times be desirable 
to take extraordinary precautions to prevent its extension, 
which would be entirely useless if the disease were estab- 
lished. This, it is true, is not the popular or legal way of 
regarding preventive measures, but it is the scientific one. 
If a case of smallpox should occur in Providence, which has 
been free from it for four years, it would be worth while, 
perhaps, to expend considerable time and money in disinfec- 
tion, even though the chance of infection from the room or 
goods might not be one in a thousand. But if there were 
hundreds of cases of measles in the city, it would be folly to 
go to the same trouble and expense for each case, even if the 
chance of infection were ten times as great. A spark in the 
dry grass should be stamped out at any cost, but it is useless 
to waste time in extinguishing the smoldering flames left here 
and there as the line of fire is sweeping across the prairie. 

Objections to Disinfection. — There are several objections 
to the present practice of terminal disinfection. One is that 
it only partially disinfects. If disinfection is to be honestly 
and efficiently applied, methods must be changed. But even 
as now practiced, disinfection is expensive. Many cities em- 
ploy disinfectors, with horses and apparatus, while their labo- 
ratory languishes, their medical inspection is poor and their 
diphtheria patients must secure antitoxin as best they can. 
Another serious objection to routine terminal disinfection is 
that it misleads the public. They are given a false sense of 
security, and they are encouraged in the old belief that it is 



INFECTION BY FOMITES 211 

things, not persons, which are dangerous. We can never suc- 
cessfully preach the truth about carriers, or teach the neces- 
sity for stricter personal cleanliness, so long as we continue 
to make so much of a fetish of the practice of disinfection. 

Cleanliness versus Disinfection. — I am here referring to 
terminal disinfection, which is often^ only a fumigation, or 
smell-producing process. The continued practice of cleanli- 
ness all through the sickness, and indeed at all times, by 
which the transference of fresh infective material may be pre- 
vented, is another matter, the value of which was considered 
in the preceding chapter. 

Conclusions. — It seems to me, in view of the considera- 
tions here presented, that we are justified in concluding that, 

1. There is no good epidemiological evidence that any 
diseases except those due to spore-forming bacteria are to any 
great extent transmitted by fomites. 

2. Judging from our experience with yellow fever most of 
the alleged evidence of infection by fomites is not to be relied 
upon. 

3. Even if all the alleged fomites infection is real, only a 
very small part of contagious disease is traceable to this 
source. 

4. The theory of fomites infection was an a priori not an 
a posteriori theory, and is no longer demanded. 

5. Other modes of transmission so much more satisfac- 
torily account for the spread of disease, that there seems to 
be really little opportunity for infection by fomites. 

6. Laboratory investigation shows that fomites infection 
with spore-forming bacteria is common; that such infection 
in typhoid fever, tuberculosis, diphtheria and with other resist- 
ant organisms doubtless sometimes takes place; that it is 
possible in cholera and plague, while such infection in gonor- 
rhea, influenza, cerebro-spinal meningitis and pneumonia 
must be practically impossible. 

7. Experiment and epidemiological observation have dem- 
onstrated that fomites infection is practically impossible 



212 THE SOURCES AND MODES OF INFECTION 

in yellow fever and is probably so in the other insect-borne 
diseases. 

8. Experiment and observation show that fomites are of 
little moment in the diffusion of bubonic plague, and of no 
moment in the extension of Mediterranean fever, both for- 
merly believed to be spread in this way. 

9. Observations made in Providence indicate that fomites 
infection is of no practical importance in the diffusion of diph- 
theria. 

Finally, it may be affirmed that the evidence has been 
rapidly accumulating that fomites infection is of very much 
less importance than was formerly believed. 



CHAPTER VI. 



INFECTION BY AIR. 



Reasons for Former Belief. — From time immemorial the 
air has been considered the chief vehicle of infection. This 
was but natural, for until recently the virus of the infectious 
diseases was believed to be gaseous, or at least readily dif- 
fusible, and readily borne by air currents. The infective 
material was supposed to be given off in the expired breath, 
and to emanate from the surface of the body and from moist 
soil and decomposing matter of all kinds. Contagious dis- 
eases were known to arise without any apparent connection 
with other cases, and what could be more natural than to 
assume that the invisible, imponderable materies morbi is 
mixed with and carried by the air? Moreover one of the 
most widespread and best known diseases, malaria, was 
shown by a great mass of clinical evidence to be an air-borne 
disease, and yellow fever, another infectious disease of great 
importance, was also on good grounds believed to be trans- 
mitted in the same manner. What seemed to be well estab- 
lished for these two diseases was assumed on much more 
slender evidence to be true of most, if not all, the infectious 
diseases. It is true in a certain sense that the two diseases 
just mentioned are air-borne, that is, they are transmitted by 
small insects, which " diffuse," as it were, from their breeding 
places and are readily wafted by air currents. It is not in 
this sense that the term air-borne is used in this chapter, but 
the inquiry here made is whether the virus of the infectious 
diseases is borne by the air, either free or attached to small 
particles of inanimate matter. 

Then, again, the first symptoms of measles, and often of 
influenza, are connected with the nose, diphtheria appears to 
be a throat disease, while consumption and pneumonia infect 

213 



214 THE SOURCES AND MODES OF INFECTION 

the lungs. What is more natural than to assume that the air 
which bathes these parts is the vehicle of infection ? But since 
it has been shown that the pneumococcus is constantly found 
in the blood in pneumonia, and has been demonstrated before 
the initial chill, and since tubercle bacilli readily reach the lungs 
through the circulation, the force of this argument is lost. 

Omitting the insect-borne diseases, let us see first what 
epidemiological evidence there is that the contagious diseases 
are air-borne. 

Smallpox Air-borne from Hospitals. — Smallpox is be- 
lieved to be more widely air-borne than is any other disease. 
The modern doctrine of the aerial transmission of smallpox 
received its greatest support from the investigations of Power 1 
in 18S1 concerning the conditions about the Fulham Hospital 
in London. That smallpox could be carried by the air long 
distances had been claimed by many before that time, for 
Dr. Waterhouse of Cambridge, more than one hundred years 
ago, believed the disease had been wafted across from Boston 
to Charlestown, though later he was inclined to deny this 
mode of transmission. Power showed that smallpox had not 
prevailed to any extent in the vicinity of the Fulham Hospital 
before the hospital was opened, and that on a number of occa- 
sions soon after it was occupied by a considerable number of 
patients the disease began to develop in the neighborhood. 
Furthermore he showed that there was a progressive decrease 
in the amount of smallpox as the distance from the hospital 
increased, the alleged influence of the hospital extending to 
at least one mile. It was furthermore shown by the doctor 
that this distribution of the disease was uniform in every 
direction from the hospital, that is, in every quadrant of the 
circle surrounding it. Later investigations at this hospital 
yielded similar data. 2 Smallpox almost always developed 
in the vicinity whenever the hospital was occupied by from 

1 Rep. Med. Off. Loc. Gov. Bd., Lond., 1880-81, X, Supl. 302. 

2 Rep. Med. Off. Loc. Gov. Bd., Lond., 1884-85, XIV, 55, 1885-86, 
XV, 111. 



INFECTION BY AIR 215 

eighty to one hundred acute cases. But on one occasion, at 
least, there was no outbreak even when the hospital was fully 
occupied. The conclusion was that when a considerable 
number, eighty to one hundred, acute cases of smallpox are 
gathered in a hospital, there is great danger that the virus 
of the disease will be carried by the air a mile or more from 
the hospital in quantity sufficient to infect persons at that 
distance. Powers considered that the hospital was thus the 
focus of infection on one occasion when there were only 
twenty patients, and at another time when there were only 
nine, of which five were acute. It was thought, from a study 
of the conditions at the time of the outbreak, that the dis- 
semination was favored by still, damp weather. A somewhat 
similar though not generally so well defined or nicely graded 
distribution of smallpox around hospitals was believed by 
many to have been demonstrated in the cases of the Homerton, 
Deptford, and Hempstead hospitals. It was natural that 
twenty-five years ago, when knowledge of modes of infection 
was far more vague than at the present time, and with such 
evidence at hand, the officers of the Local Government Board 
should have been firmly convinced of the importance of aerial 
transmission in the spread of smallpox, and that this opinion 
should have been shared by many medical officers of health. 
Subsequent to the investigations referred to above, outbreaks 
due to the spread of this disease from hospitals are said to 
have occurred, among other places, at West Ham, 1884-85, 1 
Nottingham, 1887-88, 2 Oldham, 1888 and 1892, 3 Warrington, 
1892-93/ Bradford, 1893, 5 Liverpool, 1902-03, 6 and in Gates- 

1 Rep. Med. Off. Loc. Gov. Bd., Lond., 1886-87, XVI, 97. 

2 Whitelegge, Practitioner, Lond., 1888, XLI, 65. 

3 Report on the Health of Oldham, 1892, by Niven; also Niven,Pub. 
Health, 1892-93, V, 324, 366. 

4 Gornall, Rep. on the Epidemic of Smallpox in the years 1892-93 
in Warrington, 1885, 111. 

6 Evans, Brit. M. J., Lond., 1894, II, 356. 

8 Reece, Special Rep. Loc. Gov. Bd., Lond., No. 208. 1905, Smallpox 
in Liverpool. 



216 THE SOURCES AND MODES OF INFECTION 

head and Felling, 1903-04. x In Glasgow 2 Chalmers states 
that smallpox seemed to develop around the hospital when 
it contained many patients, but that this did not invariably 
occur. When the hospital was removed to another location, 
it again appeared to be a focus of disease. Much has been 
made of the alleged aerial transmission of smallpox from the 
ships lying in the Thames below London and used for the 
reception of cases of that disease from the metropolis. Bu- 
chanan 3 and Thresh 4 attempt to show that after the ships 
were brought into use the disease was carried by the air to 
the Essex shore at Purfleet and West Thurrocks in the Orsett 
Union. It is true enough that the incidence of the disease 
was very great in these districts, but it is difficult to under- 
stand why it is not as well explained by contact infection, as 
were hundreds of similar outbreaks in England and the United 
States. The chief evidence on which the theory of aerial 
infection is based is the existence around the hospital, in 
every quadrant, of a graduated incidence of the disease. No 
such evidence is presented in this instance, and the area of 
infection attributed to the ships lies only in one direction 
from them. Smallpox appeared on the shore nearest the 
ships, and then gradually extended to a distance of two or 
three miles. This sort of extension is just what would be 
expected in contact outbreaks. If air-borne, the near and 
distant communities should have been affected at the same 
time. It was claimed by Dr. Thresh that the influence of 
the ships could be noted at a distance of four or five miles. 
It was also claimed that several vessels anchored near the 
hospital ships developed smallpox twelve days later. That 
ships leaving London during the period of the extensive out- 

1 Buchanan, Special Rep. Loc. Gov. Bd., Lond., Smallpox in Gates- 
head and Felling, 1904. 

2 J. Royal San. Inst., 1905, XXVI, 212, and Tr. Epidemiol. Soc, 
Lond., 1904-05, n. s., XXIV, 151, 244. 

3 Rep. Med. Off. Loc. Gov. Bd., Lond., 19(fc-03, XXXII, 81. 
* Thresh, Tr. Epidemiol. Soc, Lond., 1902, n. s., XXI, 101. 



IXFECTIOX BY AIR 217 

break in that city should occasionally cam- smallpox with them 
is not remarkable. Finally it was admitted that surrepti- 
tious communication with the ships occasionally occurred. 

Aerial Convection Denied by Some. — Many sanitary offi- 
cials did not, and do not, accept these conclusions, and nu- 
merous instances are given where the disease has not extended 
from hospitals. Thus Renney 1 sa3 r s that in 1883-84 he saw 
300 cases of smallpox treated in wards which were situated 
between twenty and two hundred and twenty-four feet of 
other hospital wards, schools and houses, without any exten- 
sion, though only the school was protected by vaccination. 
At another time he saw a considerable number of cases cared 
for without harm in a ward from forty to one hundred and 
thirty-eight feet from other occupied buildings. So Wilson at 
Rugby 2 had a hospital within a few yards of a much fre- 
quented road with no untoward results. At many other 
times he has seen smallpox hospitals maintained in close 
proximity to other occupied buildings without aerial trans- 
mission resulting. Boobbyer 3 treated 20 cases near a high- 
way where a thousand workmen passed daily, and not a case 
was contracted from them. Ker 4 at Edinburgh had a small- 
pox hospital in connection with a general hospital, and close to 
other institutions, and with a population of 3000 persons liv- 
ing within a mile circle. There were only 4 cases within this 
circle, of which 2 were known to be contracted elsewhere. 
Dr. Thorne Thorne 5 stated that in two instances only had 
he seen evidence of the aerial extension of smallpox from a 
hospital, namely, at Maidstone and at Stockton, while he had 
seen numerous instances where there was no extension, 
notably at Leeds and Nottingham. 

1 Renney, Jour. Roy. San. Inst., 1905, XXVI, 210. 

2 Wilson, Brit. M. J., Lond., 1905, II, 630. 

3 Boobbyer, Tr. Epidemiol. Soc, Lond., 1905, n. s., XXIV, 219. 
* Ker, Tr. Epidemiol. Soc, Lond., 1905, n. s., XXIV, 174. 

5 Thorne Thome, Rep Med. Off. Loc. Gov. Bd., Lond., 1880-81, 
X, Supl. 40. 



218 THE SOURCES AND MODES OF INFECTION 

At Manchester Niven 1 reported only 13 smallpox cases 
out of a population of over 40,000 living within a half mile 
to a mile area around the hospital and none among the 606 
persons living within the half-mile circle. Other instances 
can be given where smallpox hospitals have not infected 
their neighborhood, and these facts should have some weight, 
though according to the advocates of the theory aerial trans- 
mission is to be expected only under certain conditions of 
the atmosphere. There is not much evidence bearing upon 
this subject to be obtained in the United States, partly 
because smallpox hospitals have been much more rarely 
situated in thickly populated districts and partly because 
less attention has been given to the subject here than in 
England. 

American Evidence against Theory. — In Philadelphia it 
is claimed 2 that the hospital has been the source of smallpox 
in its neighborhood. Thus in one outbreak in the municipal 
ward in which the hospital was situated the case rate was 
61 per 10,000, nearly twice that of any other ward, and it 
decreased as the distances from the hospital increased. The 
same conditions were noted in another outbreak. 

In Boston in 1902-03 there was some discussion as to 
whether the disease spread from the hospital, which was 
on a busy street and near many occupied buildings. The 
evidence was that there was not much smallpox in the 
neighborhood, and also that contact infection from the hos- 
pital could not be excluded. 

In New Orleans 3 a large number of cases of smallpox were 
in 1900 treated in a hospital in close proximity to a dense 
population, but without evidence of extension. Dr. Theard 
writes me that his observations, extending over nine years 
since that time, have only strengthened his views then ex- 
pressed, namely, that smallpox virus is not carried from hos- 

1 Niven, Tr. Epidemiol. Soc, Lond., 1905, n. s., XXIV, 157. 

2 Rep. Bu. of Health, Phila., 1903, 29. 

3 Rep. Bd. Health of the City of New Orleans, 1900-01, 33. 



INFECTION BY AIR 219 

pitals by the air. In Brooklyn smallpox is cared for at the 
contagious-disease hospital, in pavilions about twenty feet 
from those occupied by measles and scarlet-fever patients. 
There has been no extension of the disease, though this may 
be largely due to the effort to keep the other patients well 
protected by vaccination. But there is also a considerable 
population within a mile of the hospital which has never been 
injuriously affected by it. In Providence the smallpox hos- 
pital is distant only four hundred or five hundred feet from a 
number of cottages and an excursion ground frequented by 
hundreds of persons daily. It is true that only about a dozen 
patients have ever been there at one time, but it is hard to 
understand why ten patients should not be more dangerous 
at five hundred feet than one hundred patients a mile dis- 
tant. In Detroit there has been no aerial extension of the 
disease from the hospital, though Dr. Kiefer writes me that 
there is a considerable populated area extending to within 
about six hundred feet of the buildings. 

Theoretical Objections. — I have been led to question 
this theory of the aerial transmission of smallpox for various 
reasons. From what is known of the nature of the virus of 
so many other diseases it seems highty improbable that they 
are carried any great distance by the air, and in fact it is 
only for smallpox that this mode of transmission is claimed. 
But smallpox virus is certainly solid matter, and it certainly 
after a time loses its vitality, and in all respects other than 
the one under consideration it behaves not unlike the mate- 
ries morbi that we are better acquainted with. Again, it 
would be most remarkable, if the disease extends from, say, 
one hundred cases to the distance of a mile with sufficient 
intensity to infect many persons, that it should not extend 
one hundred feet from ten cases or even from one case. Why 
should we not expect aerial infection frequently to operate 
at short distances from single cases? Yet such transmission 
does not occur unless it be with great rarity. How rare it is 
for any claim to be made that this disease has been carried 



220 THE SOURCES AND MODES OF INFECTION 

across the street from house to house, and how unique a rigid 
demonstration of such an occurrence would be! How often 
a single case in a crowded lodging house, ship's steerage, or 
hospital ward, fails to infect others! Yet we are asked to 
believe that one hundred cases can give rise to a whole circle 
of cases a half mile away. Either the amount of virus must 
depend upon the number of patients, or it must under hospi- 
tal conditions develop in some marvelous way outside of 
the body. 

Contradictions in Claims. — If the evidence adduced in 
favor of this theory is examined, several suspicious circum- 
stances are noticed. It is very curious that a material sub- 
stance should be borne by the air without reference to air 
currents ; yet in the earlier reports by Powers all evidence of 
such currents was lacking. It is true that in later reports 
the wind has been claimed as a factor, as at Gateshead and 
Felling, but the evidence in this case has been made valueless 
by more detailed search for the origin of the cases. At Liver- 
pool the disease was distributed in different directions around 
the three hospitals, so that if air-borne it must have been 
independent of air currents. Savill at Warrington even 
claimed that the virus diffused against the wind. The reports 
of the Fulham Hospital give one the impression that the 
virus of smallpox must diffuse like a gas, which certainly is not 
thinkable. If air-borne at all, it must be carried as is dust or 
as are liquid particles. If the virus does diffuse in all direc- 
tions like a gas, the intensity of the infection should diminish 
according to the square of the distance, which it did not do 
at Fulham and Liverpool. Whether it diffuses or is carried 
like solid particles, the houses nearest the hospital should be 
by far the most intensely infected. Solid particles are speed- 
ily, under ordinary conditions, precipitated to the ground, as 
one may easily note by observing a cloud of dust of any kind. 
The particles of smallpox virus ought, then, to work their 
chief havoc close to the hospital. Yet this incidence was not 
always the case, even at Fulham, and similar absence of near-by 



INFECTION BY AIR 221 

infection was noted at Stockwell 1 and Liverpool. 2 Again, 
quite a number of instances are given where large institu- 
tions, like schools, workhouses and general hospitals, have 
been located within the area alleged to have been severely 
infected from the hospital, and yet have nearly or entirely 
escaped. It is curious, too, that in the only instance I have 
noticed in which the sex of the patients in the infected area 
was given, namely Fulham, 3 twenty-four were male and 
seventeen female. As so many more men are away from their 
homes at work, a much larger female population must be 
exposed to the hospital influence, and the female patients 
ought to be more numerous than the male. In most out- 
breaks of smallpox the male patients are more numerous, 
because the men move about more, and are thus more likely 
to be exposed to cases of disease. Again, it is remarkable 
that extension should be more likely to take place from 
acute than from chronic cases. In the former it is probable 
that the moist mucous membrane is the only source of infec- 
tion, while in the latter the dried crusts are known to be 
infectious. 

Distribution of Cases Opposed to Theory. — It is thus seen 
that there are a number of facts and a number of theoretical 
considerations opposed to the theory of aerial transmis- 
sion. That smallpox is distributed with decreasing inten- 
sity around smallpox hospitals is not a demonstration that 
the hospital is the cause, for as even the advocates of the 
theory admit, such circles of infection can be drawn around 
other points in a city during epidemic times, as was indeed 
shown by Hope in Liverpool in 1902-03 and Clayton at Gates- 
head in 1903-04. In fact most outbreaks, not only of small- 
pox but also of scarlet fever and diphtheria, are in a general way 
arranged around a center, with more cases toward the center 

1 Rep. Roy. Com., Smallpox and Fever Hospitals, Lond., 1882, 92. 

2 Hope, Observations by the Med. Off. Health on the Report of 
Dr. Reece on Smallpox at Liverpool. C. Tinling & Co., 1905, 11. 

1 Rep. Med. Off. Loc. Gov. Bd., Lond., 1880-81, X, Supl. 



222 THE SOURCES AND MODES OF INFECTION 

and fewer toward the periphery. It is not remarkable that 
occasionally a smallpox hospital is found near the center of 
such a localization of disease. As favoring this chance, it must 
be remembered that the population near a smallpox hospital 
is likely to be of the poorer classes, upon whom the weight of 
this disease most often falls. That surrounding outbreaks 
occur chiefly after the hospital has been occupied, is only to 
be expected, as the hospital is occupied by a number of cases 
only in epidemic times. Much stronger evidence would be 
offered by the advocates of this theory if they could show 
that no other explanation of the origin of the cases could be 
found than hospital infection. This they are not able to do, 
and in the absence of such evidence, and in the face of the 
evidence against the theory, the theory must be considered 
not demonstrated. 

Cases often traced to Other Sources. — A good deal of 
evidence in regard to the influence of hospitals in the spread 
of smallpox was collected in England at a time when there 
was no registration of the disease, when the frequency and 
importance of mild cases were not recognized as at present, 
and when its administrative control was not so complete. 
Thus it was stated that many cases of smallpox walked to 
the Homerton Hospital to apply for admission, ambulance 
drivers stopped at public houses, children of the neigh- 
borhood rode on the steps of the ambulance and the patient's 
friends inside. It would not be surprising if, under such con- 
ditions, smallpox spread by contact — and indeed it was admit- 
ted that this was a factor. It is interesting to note that even 
Power found personal exposure the cause of nine out of thirty- 
two cases near Fulham. In many outbreaks, where there is 
no question at all of hospital infection, to trace the source of 
such a proportion of cases is all that can be expected. Again, 
in the block of houses nearest the same Fulham Hospital 
Dudfield l showed that twenty of forty-one cases were due to 

1 Dudfield, Rep. Roy. Com., Smallpox and Fever Hospitals, Lond., 
1882, 101. 



INFECTION BY AIR 223 

contact infection. According to Clayton, 1 the medical officer 
of health of Gateshead, of the fifty-six cases of smallpox 
within one-half mile of the hospital, on which Buchanan bases 
his conclusion that the disease was carried by the air, fifty- 
two were traced to contact infection. Claj'ton in his report 
on this outbreak very clearly shows the fallacy of most of 
the arguments presented by Buchanan. In Liverpool it was 
shown by the advocates of aerial transmission that within 
one-quarter of a mile of the Parkhill Hospital the rate of 
incidence of smallpox was five hundred and twenty-six per ten 
thousand houses, while in the city outside of hospital areas 
it was onl} r eighty-five. A detailed study shows that this 
apparent high rate depended on only nine patients in one 
hundred and seventy-one houses, and Hope shows that of these 
nine, four were known to be due to direct exposure to other 
cases. A careful study of the report by Reece 2 of this Liver- 
pool outbreak is well worth while by all interested in this 
subject. A most ingenious use has been made of the facts, 
but an impartial critic must see that the conclusions arrived 
at are entirely unwarranted. If one is still in doubt, he should 
read the report of Hope, 3 the medical officer of health of 
Liverpool, which clearly and briefly refutes all the arguments 
of the government inspector. 

Conclusions concerning Smallpox. — It appears that the 
evidence for the aerial transmission of smallpox from hospi- 
tals consists solely of the alleged distribution of the disease, 
at a gradually decreasing rate, around the hospital, the exist- 
ence of the cases being assumed to be otherwise unexplained. 
It will be noted : 

1. That there are comparatively few instances of such dis- 
tribution recorded. 

1 Clayton, J. Roy. San. Ins, 1905, XXVI, 199. 

2 Reece, Rep. Local Gov. Bd., Lond, No. 208, Smallpox in Liverpool, 
1905. 

3 Hope, Observations by the Med. Off. Health on the Report of 
Dr. Reece on Smallpox at Liverpool. C. Tinling & Co, Liverpool, 1905. 



224 THE SOURCES AND MODES OF INFECTION 

2. That many instances are noted where there was no such 
diffusion. 

3. That in some of the alleged instances, as at Fulham, 
Gateshead and Liverpool, a large number of the surrounding 
cases have been shown to be due to contact infection. 

4. That in the long run the amount of infection around 
the hospital should diminish according to the square of the 
distance. This it does not do, but it diminishes irregularly, 
just as it does in most outbreaks of this and other diseases 
due to contact infection. 

5. There may sometimes be contact infection from the hos- 
pital. The surrounding population is often of the poorer sort, 
and is consequently particularly subject to the disease. 
Contact infection and chance may be sufficient to account 
for those instances where a smallpox hospital is the center 
of a local outbreak. 

The evidence in favor of the aerial transmission of small- 
pox from hospitals is so slight that it should never influence 
a municipality in its selection of a hospital site. 

The success of Edinburgh, New York, many German cities, 
and the Pasteur Hospital in Paris, in caring for smallpox in 
connection with other diseases, and even in the same building 
with other patients, indicates that the theory pi aerial infec- 
tion has little basis in fact. 

Chicken Pox. — Caiger, 1 while able successfully to isolate 
scarlet fever, diphtheria and whooping cough in his hospital 
wards by the cubicle system, had several transfers of chicken 
pox, and concludes from his experience that this disease is 
frequently air-borne. 

Scarlet Fever believed to be Air-borne. — Scarlet fever also 
is generally believed to be an air-borne disease. One reason 
for this is doubtless because until recently the desquamating 
epidermis was considered to be the chief vehicle of infection. 
As the epidermis comes off to a large extent as very fine light 
particles, it was but natural to assume that these would be 
1 Rep. Metropol. Asylums Bd., 1907, 1908. 



INFECTION BY AIR 225 

readily carried by the air. Recently much clinical evidence 
has accumulated which indicates that the epidermal scales 
are not infectious, and this has in turn developed doubts as 
to the disease being commonly air-borne. Whether or not 
the epidermis is infectious, there seems to be no really good 
evidence that the disease is caused by air-borne infection. On 
the contrary, there is considerable evidence that it is not air- 
borne. 

Scarlet Fever in Hospitals. — The writer, like every health 
officer, has frequently noted that a case of this disease may 
remain in school or hospital ward for days, or sometimes for 
weeks, without another case developing, or at most only one 
or two cases. Such facts indicate that the disease is not 
easily air-borne. Visitors to fever hospitals do not contract 
scarlet fever. Thus, of three hundred to four hundred non- 
immune students who visited the scarlet-fever wards of the 
Philadelphia hospital, remaining in the ward from twenty 
minutes to an hour, not one contracted the disease. 1 Often- 
times scarlet fever does attack other patients in hospitals, 
but it is in a manner to indicate contact rather than air-borne 
infection. When contact infection is rigidly guarded against, 
as in the Pasteur Hospital in Paris and in many English 
hospitals, scarlet fever may be, and is, treated in the same 
ward with other diseases without cross infection. The failure 
of contagious disease to spread in hospitals when contact 
infection is guarded against was referred to in some detail 
in the chapter on contact infection, and is a striking demon- 
stration of the small part played by aerial infection in the 
transmission of the common contagious diseases. 

Scarlet Fever in Dwellings. — I have been much impressed 
by the fact that scarlet fever and likewise diphtheria do not 
extend from one family to another in the same house. Most 
people in Providence live in houses of two or three stories, 
rarely more, with one or two families on each floor. Of 4306 

1 Welch and Schamberg, Acute Infectious Diseases, Phila., 1905, 
346. 



226 THE SOURCES AND MODES OF INFECTION 

" other families " living in the same house with scarlet-fever 
families, only 6.8 per cent were invaded. Investigation has 
shown that with very few exceptions the infection takes place 
through close intercourse before the disease is recognized or, 
more rarely, after the isolation has been terminated. Most 
of the disease in the "other families " develops within a few 
days after the report of the primary case, and is doubtless 
due to contact infection before the disease is recognized. 
Between the end of the second week and the termination of 
isolation, the disease extends to other families in the house 
in only 0.6 per cent of the cases, and in most of these it is 
known that isolation is not carried out, and that there is free 
intercourse between the families. If the disease were air- 
borne, it would certainly pass from one family to another in 
the house, which it does not do. 

Scarlet Fever and Outdoor Air. — If scarlet fever is not 
air-borne from family to family in the house, one would not 
expect it to be borne from house to house by the air. Yet 
such a claim is sometimes made, and even that the virus of 
the disease may thus be transmitted a considerable distance. 
A number of the reports of the health department- of Phila- 
delphia contain shaded maps purporting to show an excess 
of this disease, as well as of smallpox, in those parts of the 
city near the hospital. I do not think that much value at- 
taches to such maps, for there are too many factors involved, 
and very rarely is the intensity of the disease as great close 
to the hospital as the theory demands. Moreover, around 
very many hospitals no such distribution of the disease can 
be shown. Thus Tarnissier, 1 in Paris, found that the En- 
fants Malades and Trousseau hospitals could not be con- 
sidered foci of infection. The same is true of the scarlet-fever 
wards in Providence, in Detroit and in Boston. In the latter 
city, 2 for the period studied, there were no cases of the disease 
within one-eighth of a mile of the hospital, while in the next 

1 Tarnissier, Semaine med., 1903, 267. 

2 Med. and Surg. Rep., Bost. City Hosp., 1897. 



INFECTION BY AIR 227 

eighth of a mile circle there were sixty-eight cases, in the next 
seventy-one, in the next seventy-five and in the next seventy- 
two. 

Where various contagious diseases are treated in different 
wards of the same hospital there is sometimes cross infection. 
But this occurs so irregularly as to time and place, and is so 
limited in amount, that it can scarcely be attributed to any- 
thing but contact infection. As most of the physicians and 
nurses in our contagious hospitals have no appreciation of 
what true medical asepsis really means, it is surprising that 
we see as little cross infection as we do. If scarlet fever does 
not spread within the walls of the Pasteur Hospital, it would 
indeed be marvelous if it should extend to the neighboring 
houses. If it does not pass from family to family in the same 
house, it would be most surprising if it could be wafted by the 
air over large areas around the Philadelphia Hospital. 

Diphtheria and Sewer Air. — Diphtheria was formerly be- 
lieved to be a filth disease, and it was also believed that air, 
especially sewer air, was frequently the vehicle of infection. 
Graham-Smith refers to this, 1 and shows that there is no 
foundation for this belief, and that diphtheria bacilli have 
never been found in sewer air. He says that Shattock culti- 
vated bacilli of low virulence in sewer air for two months, but 
could not thereby increase their virulence. As I was, years 
ago, prejudiced in favor of the filth origin of this disease, I 
gave the matter careful consideration in my investigation of 
cases, but was never able to find any evidence that sewer gas 
was an etiological factor. Indeed my observation of diph- 
theria and typhoid fever had as much to do with my dis- 
carding the filth and sewer-gas theories as had the slowly 
accumulating mass of bacteriological evidence. 

Diphtheria in Hospitals and Dwellings. — From an epi- 
demiological standpoint diphtheria and scarlet fever are much 
alike. As the latter disease has been supposed to be air- 

1 Nuttall and Graham-Smith, The Bacteriology of Diphtheria, 
Cambridge, 1908, 321. 



228 THE SOURCES AND MODES OF INFECTION 

borne from person to person, so has the former, and there is 
the same lack of positive evidence for both diseases ; and the 
evidence against the theory is much the same for diphtheria 
as for scarlet fever. As is stated by Graham-Smith, bacterio- 
logical evidence is all against diphtheria being an air-borne 
disease except in rare instances, yet probably most medical 
men and most health officers consider that the disease is 
commonly spread in this way. But visiting students in hos- 
pital wards do not contract it, and it does not spread when 
cases of this disease are treated in pavilions together with 
other diseases. In Providence I am certain, from a careful 
study of about eleven thousand cases, that it practically never 
extends from one family to another in a house except by per- 
sonal contact ; and it does not extend from one hospital ward 
to another through the air. At North Brother Island in New 
York there is a diphtheria ward only a few feet from a tuber- 
culosis ward, and Dr. S. A. Knopf tells me that there is no 
cross infection. Similar conditions are noted in many other 
hospitals. Yet Coutts 1 recently suggested, without any evi- 
dence, that certain cases of diphtheria were due to street dust, 
and Cornell 2 attempted to show that the development of the 
disease in a certain locality in Philadelphia was due to air- 
borne infection. At best there was in the instances reported 
by the latter only a possibility of aerial infection, with the 
probabilities very much against it, while the facts as stated 
did point very strongly to the existence of unrecognized cases 
probably spreading the disease by contact. 

Typhoid Fever and Sewer Air. — During the heyday of 
the sewer-gas theory of disease, numerous outbreaks of 
typhoid fever were supposed to have been traced to infection 
by means of air from sewers and drains. A number of typical 
reports are given by Roechling, 3 and others may be found 
scattered through medical literature. In none of these is real 

1 Coutts, Pub. Health, Lond., 1906-07, XIX, 297. 

2 Cornell, N. York M. J. [etc.], 1905, LXXXII, 1318. 

3 Roechling, Sewer Gas and Health, Lond. & N.Y., 1898, 30. 



INFECTION BY AIR 229 

proof given that the disease was thus caused; it was merely 
a plausible hypothesis. Now in the light of present-day 
knowledge of bacteria and sewer air it is no longer a plausible 
hypothesis. For years past we have been able to trace most 
of our outbreaks of this disease to water, milk, oysters or 
other food, or to contact infection. In most instances they 
could not be due to sewer air. Usually investigation shows 
that house or institution outbreaks cannot possibly be due 
to sewer air, and where such an hj'pothesis is permissible, it 
usually appears highly improbable. I see almost every year 
small house outbreaks of typhoid fever. There is rarely any 
evidence of the escape of drain air into the house, and in 
almost all instances such escape is impossible. Most of these 
house outbreaks indicate contact infection, and in none can 
contact infection be excluded. I have never seen the slightest 
evidence that typhoid fever is ever due to sewer air, though I 
began my public-health work with a fairly strong belief in 
the danger from this source and sought diligently for evi- 
dence of it. 

Typhoid Fever and Dust. — It is also claimed that infected 
dust may be the cause of outbreaks of this disease. This 
mode of infection was considered to be of some moment in 
the Spanish- American and Boer 1 wars, and certainly bacterio- 
logical evidence points to its possibility. Many outbreaks sup- 
posed to be due to dust infection have been reported. Some 
of these are referred to by Germano 2 and Visbecq 3 and in the 
Report on Typhoid Fever in the war with Spain, 4 but if the 
original reports of these outbreaks are examined it will be seen 
that the evidence is very weak indeed. Because the houses 

1 Tooth, Brit. M. J., Lond., 1900, II, 1368; Tr. Clin. Soc, XXXIV, 
1213. 

2 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXIV, 
403. 

3 Visbecq, Arch, de med. et pharm. milit., Par., 1903, XLI, 536. 

4 Abst. of Rep. on the Origin and Spread of Typhoid Fever in U. S. 
Military Camps during the Spanish War of 1898, Wash., 1900, 215. 



230 THE SOURCES AND MODES OF INFECTION 

or apartments or barracks where an excess of typhoid fever 
appears are situated not far from a place where possibly 
infected feces are deposited, it is argued that the disease is 
caused by the wind blowing over the spot alleged to be in- 
fected. Quill * reports that typhoid fever was brought to a 
certain garrison in India by a company of five thousand Boer 
prisoners, many of whom were infected. The disease con- 
tinued to spread among the prisoners for three months, until 
there were from six to eight hundred cases. Then it slowly 
appeared among the garrison, until there were twenty-four 
cases. It was supposed to be caused by dust blown from the 
latrines, though the possibility of fly-borne infection is men- 
tioned; but an extraneous source, or unsuspected contact 
infection, is highly probable, though neither is excluded or 
even mentioned. Mewius 2 gives an excellent report of what 
he considers an air-borne outbreak, but it appears rather to 
have been due to contact infection, a typical outbreak of 
what Winslow calls prosedemic infection. 

The fact that typhoid fever, dysentery and cholera 3 can 
be treated in a well-managed hospital without spreading to 
other patients is good evidence that these diseases are not 
air-borne under such circumstances. 

Infantile Diarrhea and Dust. — Newsholme, 4 judging 
largely from the fact that the summer diarrhea of infants 
occurs with greater frequency during dry seasons, and in 
towns with poor scavenging, infers that it is due, to some 
extent at least, to the infection of milk and other foods by 
dust. This also is the view of Hope, 5 who states that in 
Liverpool in six Septembers with an average rainfall of 13.8 
inches there were 373 deaths from diarrhea, while in four- 

1 Quill, Brit. M. J., Lond., 1902, I, 383. 

2 Mewius, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1896, XXIII, 
497. 

3 Woodruff, J. Am. M. Ass., Chicago, 1905, XLV, 1160. 
* Newsholme, Pub. Health, Lond., 1899-1900, XII, 139. 
6 Hope, Pub. Health, Lond., 1898-99, XI, 435. 



INFECTION BY AIR 231 

teen Septembers with 10.9 inches of rain the deaths num- 
bered 573. 

Influenza. — During the present pandemic of influenza, 
especially at its commencement, it was frequently stated that 
the disease was chiefly air-borne, and air-borne to great dis- 
tances, even across the Atlantic. This view prevailed be- 
cause the disease spread with such great rapidity, appearing 
on this side of the Atlantic at about the same time that it 
did in England, and developing almost simultaneously in a 
large number of localities. The subject has been thoroughly 
studied by Leichtenstern, 1 Parsons 2 and Schmid. The lat- 
ter's observations were in Switzerland chiefly, where he had 
ample opportunity to study the outbreak in small isolated 
communities. His work is reviewed by Leichtenstern, who 
states that the disease never developed except after the ad- 
vent of some stranger. Parsons studied the incidence of the 
disease on several thousand deep-sea fishermen and on four 
hundred offshore lighthouse keepers, and in no instance did 
the disease develop except as the result of contact with the 
sick or within two or three days after leaving shore. He 
says there is no evidence whatever that the disease is air- 
borne. Leichtenstern studied the extension of the disease to 
distant countries, and found that all the evidence pointed to 
personal contact as the only factor in its spread. Thus care- 
ful epidemiological investigation is entirely in accord with 
the findings of bacteriology, for the weak resistance of the 
bacillus makes it difficult to understand how the disease can 
be carried by the air as readily as is often alleged. This 
feebleness of the germ renders it unlikely that influenza is 
a dust-borne disease. Of course it may spread by droplet 
infection, but the increased volume of the secretions, the per- 
sistence of the bacillus after recovery and the great number 
of carriers give such opportunities for contact infection that 

1 Leichtenstern, Nothnagel's Encycl. Pract. Med., Influenza, Phila. 
and Lond., 1905, 523. 

2 Parsons, Brit. M. J., Lond., 1891, II, 303. 



232 THE SOURCES AND MODES OF INFECTION 

it is hardly necessary to attribute much importance to 
aerial infection, as the term is generally used, or to fomites 
infection. 

Poliomyelitis. — Hill, 1 from a careful study of this disease 
in Minnesota, was led to suggest the theory that this might 
be a dust-borne disease. He finds that usually outbreaks occur 
in hot, dry weather, and many cases had long exposure to dust 
infected with animal feces, especially those of the horse. 

Measles. — Measles is considered a typical air-borne dis- 
ease, at least within doors, but the experience of the Pa- 
risian hospitals shows that the danger of infection within 
wards decreases as the opportunity for contact infection is 
lessened. 2 

Infection by Air at Short Range. — Most of the discussion 
thus far has related in large part to alleged extension of 
disease through the air from apartment to apartment, or from 
house to house, or from hospital to adjoining districts. Trans- 
mission over such considerable distances might be rare or 
even impossible, and yet nevertheless the air might be the 
chief vehicle in ordinary institution or family infection. That 
it is believed to be so is indicated by the common regulation 
that a wet sheet shall be hung before the door of the sick- 
room to prevent the escape of germs, by the wearing of caps 
by visitors and the disinfection of inaccessible portions of the 
room. If we ask the reason for this universal belief in the 
importance of air-borne infection, we shall find that it is based 
entirely on theory, and that there is no clinical evidence 
at all to indicate that such a mode of infection is of any 
great importance. What evidence we have indicates rather 
that infection by means of the air is of comparatively little 
importance. 

1 Hill, Northwestern Lancet, Sept. 1, 1909 [reprint]. 

2 Grancher, Cong. Internat. de med., 1900, XIII, C.-r., Par., Sect, 
de med. de l'enfance, 478. Moizard, Bull, et mem. Soc. med. d. hop. 
de Par., 1900, 3 s., XVII, 683. Martin, Rev. d'hyg., Par., 1903, XXV, 
256; Bull, et mem Soc. med. d. hop. de Par., 1904, 3 s., XXI, 297. 



INFECTION BY AIR 233 

Reasons for Belief. — The real reasons why people gener- 
ally attach so much importance to this mode of infection are, 
first, the hearty belief in the general theory of aerial infection 
which has prevailed from remote antiquity, and, secondly, 
because infection so often takes place when there has not been 
any known contact. Contact is the most certain and obvious 
mode of infection, and other modes should not be assumed 
without good reason. The burden of proof rests on those 
who make the assumption. 

Air and Aseptic Surgery. — The history of aseptic surgery 
is very suggestive in connection with the theory of air-borne 
infection. Lister at first unquestionably considered the air 
to be the chief source of wound infection, and this view for 
awhile dominated surgical practice. Then gradually more 
and more attention was given to contact infection, contact 
with instruments, contact with the patient's own skin, con- 
tact with the operator's hands. As danger from these sources 
was more and more perfectly guarded against, surgery became 
more and more successful and aerial infection was less and 
less dreaded. A successful surgeon of my acquaintance tells 
me that he can operate with as little wound infection in a 
tenement house as in the best operating room. Ochsner 1 
says, "Air infection is not impossible, but practically no wound 
infection is to be considered except from contact." Most 
surgeons at the present time consider aerial infection of very 
little importance. Nevertheless it has been shown, as we 
shall see, that the air, even of well-constructed operating 
rooms, contains considerable numbers of living pus-forming 
bacteria. Yet they are usually not numerous enough nor 
virulent enough to infect, and unless there is some other 
source of infection the wound heals aseptically. Piis-fonning 
bacteria are quite resistant, and are by far the most numerous 
and ubiquitous of all disease germs and more likely to be 
found in the air, and the fact that they generally tail to infect 
should give pause to any claim that the much less nunicr- 
1 Ochsner, Clinical Surgery, Chicago, 1U02, 2G. 



234 THE SOURCES AND MODES OF INFECTION 

ous air-borne germs of other diseases are the chief source 
of infection. 

Sewer Air and Bacteria. — In this connection the relation 
of sewer air to the transport of bacteria should be referred to. 
Winslow J in a very valuable paper gives a brief history of 
the theories on this subject, and shows how the former ideas 
as to the great danger to be apprehended from sewer air 
gradually gave way before increasing knowledge of bacteria, 
and particularly after it was determined that these organisms 
are not readily detached from moist surfaces. From that 
time it was generally believed that sewer air had little or 
nothing to do with the extension of the infectious diseases. 
The subject, however, was reopened by Andre wes 2 and Hor- 
rocks. 3 The latter showed that under natural conditions 
B. prodigiosus and also the bacillus of typhoid fever might 
be carried by the sewer air long distances and escape at man- 
hole and soil-pipe openings. Lewis 4 also showed that sewage 
bacteria could be found in the air passing over a sewage farm, 
and also in that blowing at low tide over a beach where 
sewage was discharged. Winslow by a series of careful experi- 
ments confirmed the work of Horrocks, but went further and 
determined the number of bacteria that are transported in 
this way. He found, as have others, that mechanical splash- 
ing may produce a slight local infection of the air in immediate 
contact with the spray, but such infection extends for only 
a very short distance and persists for not more than a minute 
or two. A careful quantitative study of the air of nineteen 
different plumbing systems in various parts of Boston showed 
that very few sewage bacteria are found in such air. Those 
bacteria were found only four times in 200 liters of air, 

1 Winslow, Rep. to San. Com. Nat. Ass. Master Plumbers, 1907-09; 
Abst. Am. J. Pub. Hyg., Bost., 1909, V, 640. 

2 Andrewes, Rep. Med. Off. Local Gov. Bd., Lond., 1906-07, XXXVI, 
183, and 1907-08, XXXVII, 266. 

3 Horrocks, Pub. Health, Lond., 1907, XIX, 495. 

4 Lewis, Scot. M. & S. J., Edin., 1907, XX, 487. 



INFECTION BY AIR 235 

and then in the presence of mechanical spraying of sewage 
at the point of collection. To illustrate the paucity of dan- 
gerous bacteria in sewer air he says: 

"In a surface water of good quality, like that of New 
York City, the colon bacillus can almost invariably be iso- 
lated from ten cubic centimeters. This means a slight degree 
of intestinal pollution, but experience has shown that the 
chance of infection from such a water is but slight; and we 
drink it without serious alarm. If one were to breathe for 
24 hours the undiluted air of a house-drainage system, at 
any point not immediately infected by mechanical splashing, 
it appears that less than fifty intestinal bacteria would be 
taken in; for the daily consumption of air is about 10,000 
liters, and in 200 liters I obtained negative results from air 
of this sort. In drinking New York water twice as many 
colon bacilli are ingested every day, for 1000 cubic centi- 
meters is a small amount for daily consumption. So there 
would be less danger of contracting disease from continually 
breathing the air of a vent pipe, or of a soil pipe, except 
where liquid is actually splashing, than. from drinking New 
York water." 

Anthrax. — Some time since, while considering this subject, 
it occurred to me that anthrax ought to be air-borne more 
often than any other disease. The spores are extremely resist- 
ant, and are found in great numbers in hair, wool, etc., and 
the manipulation of these materials is quite likely to raise a 
considerable amount of dust. If this be so, and if floating 
germs are carried to the alveoli of the lungs, as is alleged, the 
pulmonary type of this disease ought to be very common. 
Formerly this seems to have been the case. According to the 
report of the Local Government Board, 1 of thirty-two cases 
occurring in the woolen industry of Bradford during nine 
months, twenty-three were of the internal type. Since then 
great effort has been made to eliminate dust as much as 
possible from the woolen and other industries in which dry 
1 Rep. Med. Off. Local Gov. Bd., Lond., 1882-83, XII, 98 



236 THE SOURCES AND MODES OF INFECTION 

infected material is handled. As a consequence, as stated, in 
the last report of the factory inspector which I have at hand, 1 
of four hundred forty-four cases of industrial anthrax in Eng- 
land from 1899 to 1907 only twenty-one were of the pul- 
monary type, and all of these twenty-one were in the dusty 
woolen industry. The disease is not nearly so common in 
the United States, owing to the fact that less infected material 
is imported, but of fifteen cases in Philadelphia two only were 
internal. Even now, under the best conditions, there must 
be considerable infected dust caused by opening and separat- 
ing the bales, and the comparative rarity of the pulmonary 
type of the disease indicates that it is not very easily air- 
borne, though it appears almost certain that some cases 
develop in this manner. Furthermore, it appears that this 
disease may be transmitted by the air even out of doors. 
Legge states that he has seen two horses infected by feeding 
where the dust from the blower of a wool-sorting room was 
discharged, and Silberschmidt 2 reported a similar infection of 
eight out of twenty-two horses near a hair factory at Zurich. 
Slight Evidence that Disease is Air-borne. — It is thus 
seen that clinical and epidemiological evidence of the spread 
of contagious diseases through the medium of the air is 
scanty. No proof of extension through the external air is 
presented for any important disease except smallpox, and 
this is far from conclusive. I have never seen any good clin- 
ical evidence that diseases are air-borne, even indoors. On 
the contrary, there is much evidence that this mode of infec- 
tion is not a common one. The reasons for the widespread 
belief in the transmission of disease through the air seem to 
be entirety theoretical, and to have been developed simply 
because no other satisfactory explanation was at hand. Let 
us now consider laboratory and experimental evidence. 

1 Report Chief Inspector of Factories and Workshops, 1904, 49; 
1905, 49; 1906, 38; 1907, 56; also Legge, Lancet, Lond., 1905, I, 841. 

2 Silberschmidt, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1896, 
XXI, 455. 



INFECTION BY AIR 237 

Bacteria not given off from Moist Surfaces. — Among 
the many new conceptions which resulted from the study of 
bacteriology, one of the most novel was that, contrary to all 
previous ideas, bacteria are not given off from and are not 
readily detached from moist surfaces or liquids in a state of 
rest. This was first shown by Nageli 1 and has been amply 
confirmed by Buchner, 2 Wernich, 3 Huhs 4 and others. 

When this became known, numerous experiments were 
undertaken to determine whether the expired air was free 
from germs, as in accordance with the newly discovered facts 
it should be. Tyndall was the first to show that bacteria 
are not found in expired air, and Gotschlich 5 cites a dozen 
or so workers, all of whom obtained only negative results 
from an examination of the expired air. According to Flugge, 6 
Cadeac and Malet, Grancher and Gennes, and Muller were 
unable to find tubercle bacilli in the ordinary expiration of 
phthisical patients, and these early observations have been 
amply confirmed by others. 

It has been shown not only that air currents are incapable 
of removing bacteria from liquids but also that such currents 
do not remove them from the surfaces of solids. Most mate- 
rials which contain pathogenic bacteria, such as culture media, 
saliva, mucus, pus, excreta, etc., present, when dry, a some- 
what hard and often glazed surface, so that it is not sur- 
prising that exceedingly strong air currents, even of sixty 
meters per second, do not remove the contained germs. This, 

1 Nageli, Die niederen Pilze, Miinchen, 1877, 107, Untersuchugen in 
die niederen Pilze, 1882. 

2 Nageli u. Buchner, Sitzungsber. d. Bay. Akad. d. Wiss., Miinchen, 
7 June, 1879. 

3 Wernich, Virchow's Arch. f. path. Anat. [etc.], Berl., 1880, LXXIX, 
424. 

* Huhs, Ztschr. f. Tuberk. u. Heilstattenw., Leipz., 1906, IX, 396. 

5 Gotschlich, Kolle u. Wassermann, Handbuch [etc.], Jena, 1902, I, 
171. 

6 Flugge, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 
107. 



238 THE SOURCES AND MODES OF INFECTION 

according to Gotschlich, 1 has been demonstrated by Nageli, 
Buchner, Wernich, Hamburger and Stern, and Flugge. Got- 
schlich says that Honssell found it impossible to detach 
bacteria from infected clothing. 

Infection in Dust. — So firmly was the theory of aerial 
infection intrenched in the minds of men, that search was 
made for some other means than the expired breath by 
which bacteria might get into the air. It was very early 
found that many bacteria could withstand drying for con- 
siderable periods of time, and it was at once suggested that 
material containing disease germs might become dry and pul- 
verized, and that the resulting infective dust might readily 
be transported by currents of air. Indeed Koch 2 was one 
of the earliest, as well as one of the strongest, supporters of 
this view. 

Resistance of Bacteria to Drying. — If dust is a vehicle 
for the transport of the germs of disease, and bacteria are 
air-borne on or in bits of dust, or float as separate particles, 
they must withstand a considerable amount of drying. That 
some species do retain their vitality and virulence after 
becoming quite thoroughly dry, has been demonstrated. Sys- 
tematic studies of the effects of drying and of light on dif- 
ferent disease-producing bacteria have been made, and almost 
every germ has been examined from this standpoint by men 
particularly interested in working out its biological characters. 
In some instances, as, for example, the tubercle bacillus, the 
experiments and observations are very numerous. In the 
chapter on fomites infection, the resistance of the different 
pathogenic organisms to dryness and to light was considered. 
While some species were shown to have very little resisting 
power, the germs surviving for a few hours or a few minutes 
only, others, like the bacilli of typhoid fever, diphtheria and 

1 Gotschlich, Kolle u. Wassermann, Handbuch [etc.], Jena, 1902, I, 
170. 

2 Koch, Mit. a. d. k. Gesundheitsamte, 1884, II, Trans. Sydenham 
Soc. Pub., CXX. 



INFECTION BY AIR 239 

tuberculosis, may, when dry, retain their vitality for months. 
In addition to the general knowledge of the resisting power of 
bacteria, which has been accumulating, special and systematic 
attempts have been made to determine directly the chances 
of infection by air-borne dust. 

Studies on the Drying of Germs. — Among the earliest 
work of this kind was that by Germano. 1 He employed room 
dust and different kinds of earth, which after sterilization 
were inoculated with cultures of bacteria grown in various 
media. He found that generally the bacteria perished sooner 
in room dust than in other materials, and that bacteria 
which, like the typhoid bacillus, might survive for months 
even when dried on clothing or solid material, would speedily 
die in a very short time in dust. After a large number of 
experiments he concluded that cholera, plague, typhoid fever, 
influenza and gonorrhea could not be dust-borne; that under 
certain circumstances, with strong air currents, streptococcus 
and the germs of pneumonia and of diphtheria might be air- 
borne, and that, besides the spores of anthrax and tetanus, 
many of the pus organisms, meningococcus and the tubercle 
bacillus, might be transported in dust. It is suspected that 
he did not employ the true coccus of cerebro-spinal meningi- 
tis, for recent workers are agreed that this bacterium has very 
weak powers of resistance. His results with the pneumo- 
coccus also are surprising, as this too is rather feeble. 

Neisser 2 in 1898 made a careful study of the strength of 
air currents necessary to move dust infected with various 
pathogenic bacteria. He showed that currents of from 1 
to 4 mm. per second are sufficient to transport room dust, 
and it was chiefly with such currents that he worked. He 
used from twenty to thirty drops of an agar culture mixed 
with 30 c.c. of sterile dust. He drew dust through narrow 
tubes in a rather complicated apparatus, and it appears that 

1 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, 
XXIV, 403; 1807, XXV, 430; 1807, XXVI, 66, 273. 

2 Neisser, Ueber Lauftstaub-Infection, Inaug. Dis., Breslau, 1898. 



240 THE SOURCES AND MODES OF INFECTION 

the conditions were too far removed from the natural to 
render the results of much value. Neisser's conclusions were 
that diphtheria, typhoid fever, plague, cholera, pneumonia, 
are not dust-borne diseases, but that spores, most of the pus 
organisms, tubercle bacilli, and the germs of cerebro-spinal 
meningitis may be so carried. It will be seen that to a large 
extent he agrees with Germano, but it is to be noted, however, 
that his tests, like those of Germano, were all culture tests, 
except those for tuberculosis, in which alone animal inocula- 
tions were made. Besides such systematic work as that of 
Germano and Neisser, much has been done in the study of 
special diseases by men particularly interested therein. 

Drying of Typhoid Bacilli. — Firth and Horrocks x found 
that the typhoid bacillus would live for 23 days in sand dry 
enough to be blown by the wind. Harrison and Harrison, 2 
working in India, recovered the organism after » 118 hours 
when kept in diffused light in very dry dust. Aldridge 3 
moistened sand with urine containing typhoid bacilli on 
three successive days, and dried it on the fourth day, and 
blew it with a bellows over sterile bouillon. He recovered 
the bacillus on the 1st, 4th and 9th day thereafter. 

Horrocks 4 showed that the micrococcus of Mediterranean 
fever would survive in dry soil for about 3 weeks. 

Drying of Diphtheria Bacilli. — Flugge 5 says that diph- 
theria bacilli perish when dry enough to be blown about in 
dust. This is confirmed by Pernice and Scagliosi and Reyes. 6 
Reyes found they would live for 14 days in dry sand. 

Drying of Plague Bacilli. — Tidswell, 7 experimenting with 
dust of various kinds, could not recover the bacillus of bu- 

1 Firth and Horrocks, Brit. M. J., Lond., 1902, II, 936, 1094. 

2 Harrison and Harrison, J. Roy. Army Med. Corps, Lond., 1904, 
II, 721. 

3 Aldridge, Indian M. Gaz., Calcutta, 1903, XXXVIII, 249. 

4 Horrocks, J. Roy. Army Med. Corps, Lond., 1905, V, 78. 

5 Flugge, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1895, XVII, 401. 

6 Cited by Germano. 

7 Tidswell, Rep. on Plague in Queensland, 1902, 67. 



INFECTION BY AIR 241 

borne plague after 11 days when the dust was dried under 
natural conditions, and it usually died within 3 or 4 days. 
When dried very slowly it lived about twice as long. Rose- 
nau 1 found that this bacillus did not live in dried bone dust 
over 6 days, and he did not recover it from dry and sterile 
garden soil after 1 day. 

Drying of Tubercle Bacilli. — More attention has been 
given to the tubercle bacillus than to any other pathogenic 
organism. Besides other experiments referred to elsewhere 
in these pages it may be mentioned that Kirstein 2 experi- 
mented with various kinds of dust, and could not find living 
tubercle bacilli after 8 days. The dust was artificially 
infected and exposed to diffused light. He thinks droplet in- 
fection far more important than dust infection. Cadeac 3 
was unable to reduce sputum to dust until it had been dried 
10 to 12 days, while the tubercle bacilli had nearly died out 
on the 6th day. Even when pulverized sputum is injected 
into animals, tuberculosis rarely develops, and it must be 
still rarer as the result of inhalation. Sticher 4 also and 
Beninde 5 found it difficult to demonstrate living bacilli 
in dried and pulverized sputum under natural conditions. 
Nevertheless most observers do find living tubercle bacilli in 
dust, though usually with weakened virulence. 

Drying of Cholera Spirilla. — According to Germano, chol- 
era spirilla may sometimes survive in dust for 3 days, but 
oftentimes they die in 1 day. He says that Honssell was 
never able to obtain living spirilla from infected dust, 
though Uffelmann was able to do so for a short period. 

1 Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. 
Xo. 4, 1901. 

2 Kirstein, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1905, L, 186. 

3 Cacteac, Lyon Med., 1905, CV, 893; also Lyon Med., 1908, CXI, 
532. 

4 Sticher, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 
163. 

5 Beninde, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 
193. 



242 THE SOURCES AND MODES OF INFECTION 

William 1 believes that cholera cannot be a dust-borne 
disease. 

Tubercle Bacilli in Dust. — Of more practical importance 
than experiments with artificially infected dust is the deter- 
mination of the presence or absence of disease-producing 
bacteria in supposedly infected localities. The chief interest 
in such investigations has centered in tuberculosis. Cornet 2 
has made a more extensive study than any one else of the 
natural distribution of tubercle bacilli in dust. He examined 
147 specimens of dust collected from hospital wards, dis- 
pensaries, private houses, streets, etc. No bacilli were found 
in the street or in places not occupied by the tuberculous, 
and even in the environment of the consumptive germs were 
found only when the patient was careless in the disposal of 
sputum. Cornet's observations have been confirmed by Rem- 
bold, Kriiger, Kastner, Ballinger, Kusterman, Le Noir and 
Camus and Enderlin, besides others elsewhere referred to. 
Gotschlich 3 examined one hundred and nineteen specimens 
of dust from streets and public places and was not able to 
demonstrate the presence of tubercle bacilli. While most 
observers have been unable to find the tubercle bacillus in 
street dust, it is said to have been found by Manfredi * and 
Schnirer. 5 Prausnitz 6 and Petri 7 obtained tubercle bacilli 
from the dust in railway carriages, and Bissell 8 found them 
in tram cars in Buffalo. 

1 William, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., 1893, XV, 166. 

2 Cornet, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1885, V, 98; 
Nothnagel's Encyclopedia of Pract. Med., Phila. & Lond., 1907, Tuber- 
culosis, 85. 

8 Gotschlich, Die Verbreitung der Tuberkelbacillen in Staub von 
R'aumen mit starkem Menschenverkehr, Inaug. Dis., Breslau, 1903. 

4 Manfredi, Jahresb. u. d. Fortschr. . . . d. path. Mik., Baumgarten, 
1891, VII, 570. 

6 Schnirer, Wien. med. Presse, 1891, XXXII, 3. 

6 Prausnitz, Arch. f. Hyg., Munchen u. Leipz., 1891, XII, 192. 

7 Petri, Arb. a. d. k. Gesund.-Amt., Berl., 1894, IX, 76. 

8 Bissell, N. York M. J., 1895, LXII, 783. 



INFECTION BY AIR 243 

Some observers have not found the bacilli so numerous as 
did Cornet. Thus Hill, 1 following Cornet's methods, obtained 
virulent bacilli in but 5 of 496 swabbings from private 
houses where there were cases of the disease, and in 3 of 
180 swabbings from hospital wards. 

Heymann 2 has criticised Cornet's findings on the ground 
that the latter recovered the dust by means of moist swabs, 
thereby perhaps taking up many bacilli which were attached 
to the floor, table, etc., and which would not therefore have 
any part in air-borne infection. He does not find living 
bacilli so numerous in dust as did Cornet. Heymann in 120 
tests found them only one-third as often, but Coats, 3 follow- 
ing Heymann's methods, was able by inoculation tests to 
demonstrate the presence of tubercle bacilli in 66 per cent of 
specimens of dust obtained from fourteen rooms occupied by 
tuberculous patients. On the whole, it appears that virulent 
tubercle bacilli are quite commonly found in the dust of 
rooms occupied by careless tuberculous patients. 

In this connection may be mentioned an experiment of 
Heymann's in which he rubbed and shook a sputum-infected 
handkerchief, after two days' drying, in a closed box, and 
found floating bacilli after the lapse of an hour. 

Meningococcus in Dust. — Jaeger 4 claimed to have found 
the meningococcus on the floor of barracks, and Netfcer 5 the 
pneumococcus in the dust of a sick-room four weeks after the 
case was removed, but from what is now known of the resist- 
ance of these bacteria this is highly improbable. Wash- 
bourn and Eyre 6 found the pneumococcus in dust from a 
ward and laboratory at Guy's Hospital, but failed to find it in 

1 Hill, Am. Pub. Health Ass. Rep., 1902, XXVIII, 209. 

2 Heymann, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1901, 
XXXVIII, 21. 

3 Coats, Trans. Brit. Cong, on Tuberculosis, 1901, I, p. 88. 

4 Jaeger, Deutsche med. Wchnschr., 1899, XXV, 472. 

5 Netter, Compt. rend. Soc. de biol., Par., 1897, IV, 538. 

6 Washbourn and Eyre, Lancet, Lond., 1902, II, 1440. 



244 THE SOURCES AND MODES OF INFECTION 

street dust. Washbourn says that it has also been found in 
dust by Emmerich, Maximowitch and Netter. 

Diphtheria Bacilli in Dust. — These bacilli have been found 
in the dust of a scarlet-fever ward, 1 and are said to have been 
found in a diphtheria ward by Richardiere and Tallemer, 2 
but Schlichter 3 could not find them in a hospital in Vienna. 
Cobbett 4 exposed plates in a diphtheria ward, but could 
obtain no bacilli except when the plates had been touched 
by the fingers of the patients. 

Dust and Other Diseases. — There has been much dis- 
cussion of late in England about the necessity for disinfecting 
schoolrooms, and examination of school dust has shown the 
presence of colon bacilli 5 and the pus organisms. 6 

General Conclusions. — While these facts relating to the 
resistance of disease germs to drying, and their presence in 
supposedly infected localities, afford no definite information 
as to the danger to be apprehended from infection by air- 
borne dust, they do lead to some tentative conclusions. It 
is scarcely possible that gonorrhea, influenza, cerebro-spinal 
meningitis and pneumonia can be dust-borne. It is possible, 
perhaps, but highly improbable, that plague and cholera can 
be so borne. The bacteriological evidence indicates that the 
germ of typhoid fever, dysentery, Mediterranean fever, diph- 
theria, tuberculosis and suppuration may be carried by float- 
ing dust, and it is certainly possible for anthrax and other 
spores. 

Danger from Dust Slight. — Bacteriology also teaches what 
is often forgotten, that pathogenic bacteria, with the ex- 
ception of spores, die off quite rapidly when dried, and that 
the survivors usually have a weakened virulence. If in a 

1 Renney, Pub. Health, Lond., 1905, XVII, 706. 

2 Richardiere et Tallemer, Gaz. d. mal. enfant [etc.], Par., 1899, X. 

3 Schlichter, Arch. f. Kinderh., Stuttg., 1892, XIV, 129. 

4 Cobbett, J. Royal San. Inst., Lond., 1904, XXV, 405. 

5 Hewlett, Lancet, Lond., 1909, I, 741, 815, 889. 
a Kerr, Med. Off. Educa., Lond., 1908, 31. 



INFECTION BY AIR 245 

sick-room or hospital ward the germs of disease are scattered 
so freely on the floor or room contents that enough of them 
can survive drying and pulverization to float in the air and 
cause disease, the opportunities for contact infection with the 
comparatively fresh infective material must be very great, so 
great, it seems to me, that infection by air under such condi- 
tions must be very insignificant or entirely negligible as com- 
pared with infection by contact. 

Droplet Infection. — Another way in which living bacteria 
may be carried by the air is in tiny floating particles of liquid. 
Fliigge 1 was the first to call attention to the fact that during 
speaking, and especially during loud talking, coughing and 
sneezing, tiny droplets of saliva are thrown off from the 
mouth. Indeed such droplets may be readily seen in the 
proper light, and it hardly needed special experiment to prove 
their existence. Nevertheless, Fliigge 2 and Laschtschenko, 3 
by infecting the mouth with B. prodigiosus, showed that 
germ-carrying droplets are, during coughing, borne to a dis- 
tance of nine meters in front of the mouth. These droplet 
experiments have been repeated with confirmatory results by 
Goldie, Esmarch, B. Frankel, Moller, Hiibner, Weismayr and 
Koniger, and the last mentioned has shown that the droplets 
may be found two meters behind the person coughing. 4 
Goldie showed that in fourteen per cent of the cases tubercle 
bacilli could be caught on plates after a single act of coughing. 
Every patient examined at one time or another gave positive 
results. No bacilli were found, even as near as six inches, 
during deep breathing, but after coughing they could be 
recovered from all parts of the room. 

1 Fliigge, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXV, 
179. 

2 Fliigge, Ztsch.f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 107. 

3 Laschtschenko, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, 
XXX, 125. 

4 Koniger, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1900, XXXIV, 
119. 



246 THE SOURCES AND MODES OF INFECTION 

Amount of Droplet Infection. — Since it has been shown by 
Fliigge that droplets from speaking may float for from five 
to six hours, and be transported by air currents of only one 
mm. per second, it is not surprising that they should be car- 
ried such distances. Nor is it surprising that Hutchinson 1 
was able to prove that a fine spray of a culture of B. pro- 
digiosus was carried fifty-five meters along a corridor, and up 
two flights of stairs, and also a considerable distance out of 
doors. Others have shown that the bacteria of the mouth 
may be carried by the air during speaking over a large room 
or hall. 2 Leon 3 showed that in speaking three hundred 
words 250,000 bacteria were thrown off from the mouth, and 
Ziesche 4 found over 20,000 tubercle bacilli on a plate 324 
sq. cm. exposed for half an hour. But it has further been 
shown by Kirstein 5 and Koniger 6 and Laschtschenko 7 that 
the size of the droplets and the distance they can be carried 
depend to a large extent upon whether the liquid is thin and 
watery or a thick mucus. Hence we should expect that 
droplets of thick sputum would not be carried nearly so 
far as droplets of more liquid saliva, and according to 
Goldie 8 droplets of the saliva rarely carry bacilli but only the 
droplets of sputum. 

Quantitative Experiments. — Since the above was written 
Winslow and Robinson 9 have published a very interesting 

1 Hutchinson, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1901, 
XXXVI, 223. 

2 Gordon, Rep. Med. Off. Local Gov. Bd., Lond., 1902-03, XXXII, 
421. 

3 Leon, Arch. f. klin. Chir., Berl., 1903-04, LXXII, 904. 

4 Ziesche, Ztschr. f . Hyg. u. Infectionskrankh, Leipz., 1907, XLVII, 50. 

5 Kirstein, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1900, XXXV, 
123. 

6 Koniger, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1900, XXXIV, 
119. 

7 Laschtschenko, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, 
XXX, 125. 

8 Goldie, Canadian Pract. & Rev., Toronto, 1899, XXIV, 433. 

9 Winslow and Robinson, Jour. Infect. Dis., Chicago, 1910, VII, 17. 



INFECTION BY AIR 247 

paper on this subject giving an excellent resume of previous 
investigations. They repeat the experiments of some of the 
European writers, and like them they find that if the mouth 
of a speaker is infected with a specific germ, as B. prodigiosus, 
agar plates exposed in different parts of the room show nu- 
merous colonies of the bacillus. They also, by the exposure 
of plates in the room with the speaker, recovered Gordon's 
Streptococcus salivarius, which is a normal inhabitant of the 
mouth. The authors emphasize the distinction noted by 
others between the larger droplets of mouth spray which con- 
tain the most bacteria and which settle out of the air in the 
space of a few feet from the mouth and the smaller droplets 
which float for a longer time and may pass to some distance 
from the speaker, and which alone may be considered as prop- 
erly constituting an infection of the air. The chief interest 
in their studies attaches to their quantitative work carried 
out on the lines devised by Winslow for his investigations of 
sewer air. Out of 140 liters of air taken at various points in 
the room immediately after 10 to 50 minutes' loud speaking 
by a person whose mouth was infected with B. prodigiosus, 
the bacillus was found seven times. Of 74 liters examined for 
Streptococcus salivarius none were found to contain this nor- 
mal inhabitant of the mouth. The authors consider that an 
artificial infection of the mouth may give too high an index 
of air contamination, while the normal germs of the mouth 
may be thrown off in smaller numbers than are the disease 
germs from sick persons. The authors conclude that these 
experiments furnish "no basis for a belief that tuberculosis 
or any other disease is contracted to an appreciable extent 
through the inspired air " and are " in harmony with the 
conviction now generally gaining ground that aerial infection 
of any sort is a minor factor in the spread of zymotic disease." 
Lepra Bacilli. — Schaffer l was able to recover bacilli from 
a leprous patient by holding cover glasses a short distance in 
front of the face while the patient was speaking and coughing. 
1 Schaffer, Arch. f. Dermat. u. Syph., Wien, 1898, XLIV, 159. 



248 THE SOURCES AND MODES OF INFECTION 

Pneumococcus. — Wood ! found that pneumococci did not 
retain their vitality in floating droplets over one hour, and 
not half an hour in diffused light. 

Influenza Bacilli. — According to Gotschlich, 2 droplets con- 
taining influenza bacilli will float for five hours. Very little 
has been done to demonstrate the existence of infected drop- 
lets in any other diseases. 

Bacteria found in Air. — Having shown that bacteria may 
float in the air on particles of dust and in droplets of liquid, 
we must next inquire whether pathogenic germs have actually 
been found in the air. Graham-Smith 3 examined the air ©f 
the House of Commons for pathogenic bacteria with negative 
results, as did Andre wes 4 and Gordon 5 the air in the streets 
of London. Little light is thrown on our present problem 
by these and similar negative tests of outdoor air or of air 
away from the vicinity of the sick. Far more interest and 
value attach to the examination of air in the vicinity of 
cases of infectious sickness. 

Tubercle Bacilli in Air. — Heymann 6 was able to recover 
virulent tubercle bacilli from the air of a small chamber in 
which was placed a coughing tuberculous patient. Similar 
results were obtained by Laschtschenko. 7 Corbett 8 recovered 
acid-fast bacilli from the ventilating shaft of a hospital, but 
made no inoculation tests. Klein 9 infected guinea pigs by 
exposure in the vent shaft of Brompton Hospital. According 

1 Wood, J. Exper. M., N. Y., 1905, VII, 592. 

2 Gotschlich, Kolle u. Wassermann, Handbuch [etc.], Jena, 1902, 1, 175. 

3 Graham-Smith, J. Hyg., Cambridge, 1903, III, 498. 

4 Andrewes, Rep. Med. Off. Local Gov. Bd., Lond., 1906-07, XXXVI, 
187. 

5 Gordon, Rep. Med. Off. Local Gov. Bd., Lond., 1902-03, XXXII, 
421. 

6 Heymann, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1901, 
XXXVIII, 21. 

7 Laschtschenko, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, 
XXX. 

8 Corbett, St. Paul M. J., St. Paul, Minn., 1904, VI, 735. 

9 Stevenson and Murphy, Hygiene and Public Health, II, 212. 



INFECTION BY AIR 249 

to Cornet and Meyer, 1 Williams, Celli and Guarnieri, Wehde, 
and Baumgarten have examined air for tubercle bacilli with 
negative results. Recently Le Noir and Camus 2 demon- 
strated by inoculation tubercle bacilli in the dust of a hospi- 
tal ward, but they could not obtain them by the filtration 
of even 53,000 liters of the air. Viewing the human nose as 
a filter, they took swabbings from the nose of physicians and 
attendants of phthisical patients, but could not demonstrate 
tubercle bacilli by inoculation, though they found them in 
the nose of the patients themselves. Cornet considers that 
the germs are so sparsely distributed that one ought not to 
expect to obtain them by the filtration of even 1000 liters 
of air. He says that the finding of tubercle bacilli in settled 
dust has as much bearing on air infection as finding it in 
the air and is a much easier operation. It does not appear 
that Cornet is correct in his contention that the examination 
of dust is of more practical importance than the examination 
of air. The examination of dust can throw no light on the 
number of bacteria floating in the air at any one time, and 
as Winslow in his work on sewer air previously referred 
to has so clearly pointed out, a quantitative examination of 
the floating bacteria is necessary if we wish to determine the 
real danger from the inhalation of the air. No such enumer- 
ation of tubercle bacilli seems to have been made, and the 
difficulty of finding them suggests that they are not very 
numerous, even in the vicinity of patients, and that perhaps 
the air of a room is not always dangerous to breathe even if 
tubercle bacilli can be found in the settled dust. 

Pus-forming Bacteria in Air. — Numerous observers are 
referred to by Gotschlich, 3 Friedrich 4 and Noeggerath 5 as 

1 Cornet and Meyer, Kolle u. Wassermann, Handbuch [etc.], Jena, 
1903, II, 143. 

2 Le Noir and Camus, Comp. rend. Soc. de biol., Par., 1908, LXV, 
464, 622; Ann d'hyg. et de meU colon., Par., 1908, 4 s., IX, 74. 

3 Gotschlich, Kolle u. Wassermann, Handbuch [etc.], Jena, 1902,1, 176. 

4 Friedrich, Arch. f. klin. Chir., Berl., 1898, LVII, 288. 

5 Noeggerath, Deutsche Ztschr. f. Chir., Leipz., 1900-01, LV1II, 277. 



250 THE SOURCES AND MODES OF INFECTION 

having found various pus-forming bacteria in the wards and 
operating rooms of the hospitals. Among more recent Ameri- 
can writers may be mentioned Robb, 1 Rosenow, 2 Monks 3 and 
Harrington. 4 The latter found that Petri dishes exposed in 
an operating room in Boston always contained pus organisms. 
The maximum was 131 per square inch per hour. Gordon 5 
found staphylococci in an operating room in England, also in 
a barber's shop, and they have been demonstrated in the air 
by Hamilton. 6 Gordon could not find them in the open air, 
but they have been found in the air of streets by others. 7 

Other Bacteria in Air. — Concornotti 8 reports that he 
found pneumonia germs in the air of the Hygienic Institute 
of Cagliari. 

Beck 9 found swine plague bacilli in the air of a laboratory 
where experiments with that germ were being carried on. 

Bruce 10 could not find the germ of Mediterranean fever in 
air-borne dust in Malta. 

Actual Danger of Infection by Air. — Pathogenic bacteria 
may withstand drying and the pulverization of the dried 
material, and they may be actually found floating in the air, 
yet they may not after all be dangerous, either because they 
have wholly or partially lost their virulence, or because they 
are too few in number, or for some other unknown reason. 

Little Infection of Wounds by Air. — It has been shown 
that notwithstanding the presence of considerable numbers 

1 Robb, Am. J. Obst., N. Y., 1909, LX, 451. 

2 Rosenow, Am. J. Obst., N. Y., 1904, L, 762. 

3 Monks, Ann. Surg., Phila., 1904, XL, 466. 

4 Harrington, Ann. Surg., Phila., 1904, XL, 475. 

5 Gordon, Rep. Med. Off. Local Gov. Bd., Lond., 1904-05, XXXIV, 
387. 

6 Hamilton, J. Am. M. Ass., Chicago, 1905, XLIV, 1108. 

7 Newman, Bacteriology and the Pub. Health, Lond., 1904, 78. 

8 Concornotti, Centrlbl. f. Bakteriol. [etc.], Jena, 1899, XXVI, 492. 

9 Beck, Jahresb. u. d. Fortschr. . . . d. path. Mik., Baumgarten, 
1891, VII, 567. 

10 Nature, Lond., 1908, LXXVIII, 40. 



INFECTION BY AIR 251 

of bacteria in the air of operating rooms, the aerial infection 
of wounds is of no practical importance. One reason for this 
failure to infect has been shown by Friedrich 1 and Noeg- 
gerath. 2 The conclusion of these authors is that drying and 
exposure to light so weaken the bacteria that they are not 
able to withstand the actively hostile influences of the tissues 
of the human body, though they may be able slowly to vege- 
tate on the more favorable culture media of the laboratory. 
This lowering of virulence by drying and exposure to light 
may be of great practical moment in preventing infection by 
air. So also, though other pathogenic bacteria may be 
demonstrated in the air, it may be that they are usually 
too few in number to infect. 

Experiments with Tuberculosis. — The experiment of 
Bernheim, 3 in which he was not able to infect animals with 
mouth spray over 25 cm. from the mouth, but was able to 
collect tubercle bacilli on agar plates at the distance of a 
meter, is most suggestive of the importance of the number 
of bacteria as a factor in infection. The proper way to de- 
termine the infectivity of the air is by animal experiment 
or, better still, by carefully conducted observations on human 
beings. Except in tuberculosis very few experiments of this 
kind have been made. Much, however, has been done with 
that disease. 

Tappeiner 4 had, even before the discovery of the tubercle 
bacillus, shown that tuberculosis could be produced in dogs 
by causing them to breathe dry and pulverized tuberculous 
sputum. Bertheau, Veraguth, Weichselbaum and French, 
like Tappeiner, succeeded in infecting animals by causing 
them to inhale pulverized sputum containing tubercle bacilli, 
while Koch, Cornet, Gebhardt and Preyss accomplished the 

1 Friedrich, Arch. f. klin. Chir, Berl., 1898, LVII, 288. 

2 Noeggerath, Deutsche Ztschr. f. Chir., Leipz., 1900-01, LVIII, 277. 

3 Bernheim, Clinique, Brux., 1905, XIX, 346. 

4 Tappeiner, Virchow's Arch. f. path. Anat. [etc.], Berl., 1880, 
LXXXII, 353. 



252 THE SOURCES AND MODES OF INFECTION 

same results by the use of dried bacilli obtained from cul- 
tures. More recently Cornet 1 reports a still more striking 
experiment. In a room of seventy-six cubic meters capacity, 
48 guinea pigs were exposed in cages at various heights 
above the floor. Sputum was placed on a carpet, and after 
it was dry the carpet was shaken so that the dust rose up 
in clouds. This was repeated on four days. The result was 
that 47 of the 48 animals developed tuberculosis within two 
months. Kuss 2 carried on experiments very similar to those 
of Cornet and with similar results. Kohlisch, 3 while admit- 
ting that tuberculosis may be caused by the inhalation of dust, 
claims that his experiment shows that enormously larger 
quantities must be inhaled than are necessary when a spray 
is employed. While B. prodigiosus is not pathogenic, it has 
been used by various workers for studying the penetration 
of bacteria into the respiratory tract. Nenninger, 4 using 
both infected dust and a sprayed culture, found that the 
germs were quickly carried to the smallest bronchioles. 

Dust Infection Questioned. — The contention that pul- 
monary tuberculosis ma}' be caused by the inhalation of dust 
containing tubercle bacilli was not to go unchallenged. Sirena 
and Pernice, de Toma, Celli and Guarnieri, and Cadeac and 
Malet were unsuccessful in their attempts to produce the 
disease in this way. But perhaps Fliigge 5 more than any 
other has cast discredit on this theory of the origin of pul- 
monary tuberculosis. He was unable to induce infection by 
causing animals to inhale tuberculous dust, and states that the 
dust is not carried to the alveoli. He also developed the 
theory of droplet infection, which has been received with much 

1 Cornet, Verhandl. d. Berl. med. Gesellsch., 1899, XXX, 2 Th., 91. 

2 Kuss, Sixth Internat. Cong, on Tuberc, Wash., 1908, I, 101. 

3 Kohlisch, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1908, LX, 
508. 

4 Nenninger, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1901, 
XXXVIII, 94. 

5 Fliigge, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 
107. 



INFECTION BY AIR 253 

favor, and did much to break down the almost universal 
view that dust is the chief vehicle of infection in this disease. 
Again when Koch in 1901 by his pronunciamento, that human 
tuberculosis is never caused by the milk of tuberculous ani- 
mals, stimulated a great number of workers to attempt to 
prove the contrary, evidence began to accumulate that tuber- 
culous infection of the lungs might be brought about in vari- 
ous ways, and facts came to light which told against the view 
that direct infection by means of dust is the only manner 
in which pulmonary tuberculosis can be caused. 

Dust versus Droplets. — According to the school of Flugge, 
infection by droplets is much more likely to take place than 
infection by dust, and his pupils have demonstrated the 
presence of the bacilli in the lungs immediately after inhala- 
tion. Findel, 1 working in his laboratory, has shown that the 
inhalation of even so small a number as 62 germs is sufficient 
to cause the disease, and he asserts that several million times 
as many bacteria are necessary to infect when taken by the 
stomach. Laschtschenko 2 and Heymann, 3 working under 
the direction of Flugge, were able to infect guinea pigs with 
tuberculosis by causing them to breath directly in front of the 
mouth of phthisical patients while the latter were coughing. 
The pigs were not infected when distant over one meter. 
Flugge 4 himself infected 6 of 25 guinea pigs in this manner, 
holding them distant from twenty to forty-five cm. from the 
mouth of the patient. Pfeiffer and Friedberger 5 sprayed 
guinea pigs with a culture containing 35,000 tubercle bacilli to 

1 Findel, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1907, LVII, 
104. 

2 Laschtschenko, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, 
XXX, 125. 

3 Heymann, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 
139. 

4 Flugge, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 
107. 

5 Pfeiffer and Friedberger, Deutsche med. Wchnschr., 1907, XXXIII, 
1577. 



254 THE SOURCES AND MODES OF INFECTION 

the c.c. The animals were held for ten minutes at a distance 
of eight to twenty cm. in such a manner that their bodies 
were perfectly protected. Those held at the greater distance 
did not contract tuberculosis, but the others developed what 
appeared to be primary tuberculosis of the lungs. Bartel 
and Neumann, 1 after spraying guinea pigs with tubercle 
bacilli, found the germs immediately in mouth, throat and 
lungs. Bernheim 2 infected guinea pigs at the distance of 
not over twenty-five cm., but he was able to collect tubercle 
bacilli on agar plates at the distance of one meter from the 
mouth. So also Kuss and Lobstein, 3 carrying out very care- 
ful inhalation experiments with a sprayed culture of tubercle 
bacilli, very easily and constantly developed pulmonary 
disease. Kovacs, 4 after inhalation experiments with tubercle 
bacilli, could immediately recover them from the lungs. But 
he thinks that they may also pass from the mouth to the 
lungs via the cervical and bronchial glands. Cobbett, 5 em- 
ploying sprays both of B. prodigiosus and of the tubercle 
bacillus, reports that the bacteria are carried to the periph- 
ery of the lungs by the inspired air. 

The Inhalation of Bacteria. — On the other hand, Hewlett 
and Thompson 6 found that inhaled bacteria were not carried 
even as far as the trachea, as Hildebrandt 7 had found before. 
Hartl and Herrmann 8 showed that inhaled germs decreased 
very rapidly back from the nose, and they consider that the 
upper passages are frequently the place of entrance for the 
infection, and that bacteria are rarely carried by the air to 

1 Bartel and Neumann, Wien. klin. Wchnschr., 1906, XIX, 167, 213. 

2 Bernheim, Clinique, Brux., 1905, XIX, 346. 

3 Kuss and Lobstein, Bull, med., Paris, 1907, XXI, 821. 

4 Kovacs, Beitr. z. path. Anat. u. z. allg. Path., Jena, 1906, XL, 281. 
6 Brit. M. J., Lond., 1909, II, 867. 

6 Hewlett and Thompson, Lancet, Lond., 1896, I, 86. 

7 Hildebrandt, Beitr. z. path. Anat. u. z. allg. Path., Jena, 1887, II, 
411. 

8 Hartl and Herrmann, Wien. klin. Wchnschr., 1905, XVIII, 798. 



INFECTION BY AIR 255 

the lungs. Vallee ! carried on spray experiments without 
result, and Calmette and Guerin, 2 in a few experiments made 
with infected dust, did not find that the bacilli reached the 
alveoli. Weleminsky 3 could find no bacilli in the lungs of 
guinea pigs immediately after they had been subjected to 
inhalation experiments. 

Lack of Agreement among Investigators. — Thus it is seen 
that the school of Cornet claims that pulmonary tuberculosis 
is almost always caused by the passage of infected dust to the 
alveoli, and that infected droplets are of little moment; while 
Fliigge and his pupils attempt to show that dust rarely reaches 
the alveoli but that the inhalation of droplets is the easiest 
method of causing the disease. The unprejudiced reader 
must conclude that infection in either way is possible, but 
the conditions of the experiments are so far removed from the 
natural that there must be much hesitation before assuming 
that this work indicates in any degree the common mode of 
infection in human beings. 

Bacilli may pass from Stomach to Lungs. — It is com- 
monly assumed that because pulmonary tuberculosis begins 
in the apices of the lungs the bacilli must be carried directly 
to the alveoli by the inspired air. Moreover most patholo- 
gists consider that evidence points to the alveolar surface as 
the starting point of the disease, and that the relative age of 
the lesions in the lungs and the glands indicates that it is 
primarily a pulmonary disease. The writer is not competent 
to discuss the findings of the pathologists, but there are a 
large number of careful observers who believe on pathological 
and experimental evidence that the bacilli which cause pul- 
monary tuberculosis may find their way through the lymph 
and the blood from any part of the alimentary tract to the 
lungs. Some pathologists believe that the disease begins 
in the capillaries rather than in the alveoli. Calmette and 

1 Valine, Ann. d. l'Inst. Pasteur, 1905, XIX, 619. 

2 Calmette and Guerin, Ann. de l'Inst. Pasteur, 1905, XIX, 601. 
■ Weleminsky, Berl. klin. Wchnschr., 1905, XLII, 743. 



256 THE SOURCES AND MODES OF INFECTION 

Guerin * say that primary tubercle of the lungs always be- 
gins in the capillaries, and never in the alveoli, and Aufrecht 2 
from his pathological studies comes to the same conclusion. 

Even pulmonary anthracosis may be caused by the inges- 
tion of particles of carbon. Vansteenburgh and Grysez 3 
caused animals to breath air loaded with soot from a smoky 
lamp, and though the nose was filled with soot, none was found 
in lungs or even trachea. If the experiment was prolonged, 
carbon appeared in the lungs, but not if the esophagus was tied. 
When one bronchus was occluded, the carbon appeared in the 
parenchyma of the lung just the same, provided the esoph- 
agus was open. Whitla 4 fed animals with carbon and bacilli, 
and both were found in the lungs in from four to twenty-four 
hours. Feeding was done with a tube, with great care to 
prevent inhalation. Hutchens 5 fed guinea pigs with coal 
dust, and also injected it into the abdomen, and found it in 
the lungs in three days. Grober, 6 after injecting India ink 
into the tonsils, was able to find the pigment in the lungs 
in a short time. He thought that he could trace a continu- 
ous lymphatic route from the tonsils to the costal pleura, 
whence the particles passed directly to the parietal pleura 
and the lungs. But such a connection has been denied by 
Beitzke, 7 Wood 8 and others. 

Schultze 9 denies that pulmonary anthracosis can be pro- 

1 Calmette and Guerin, Ann. de Tlnst. Pasteur, 1906, XX, 609. 

2 Aufrecht, Deutsches Arch. f. klin. Med., Leipz., 1908, XCIV, 308. 

3 Vansteenburgh and Grysez, Ann. de l'lnst. Pasteur, 1905, XIX, 787. 

4 Whitla, Brit. M. J., Lond., 1908, II, 61. 

6 Cited by Oliver, Brit. M. J., Lond., 1908, II, 481. 

6 Grober, Die Tonsillen als Eintrittspforten fur Krankheitserreger, 
Abdruck aus dem klin. Jahrb., Berl., 1905, XIV, 547. 

7 Beitzke, Virchow'sArch.f. path. Anat. [etc.], Berl., 1906, CLXXXIV, 
1; Berl. klin. Wchnschr., 1908, XLV, 1235. 

8 Wood, Rep. Henry Phipps Inst. Study . . . Tuberculosis, Phila., 
1906, IV, 163. 

9 Schultze, Miinchen med. Wchnschr., 1906, LIII, 1702. 



INFECTION BY AIR 257 

duced by feeding, as is claimed by the French experimenters, 
and insists that during the feeding some inhalation takes place, 
and that if the animals are fed through a gastric fistula with 
adequate precautions, the fragments are not carried to the 
lungs. 

A large number of workers have certainly demonstrated 
that pulmonary tubeiculosis may be caused by infection 
through different portions of the alimentary canal. 

The work of Calmette and Guerin 1 shows that tubercle 
bacilli are speedily carried from the intestines to the lungs. 

Schroeder and Cotton 2 have shown that pulmonary disease 
develops no matter in what part of the body tubercle bacilli 
are inoculated, and in Bulletin 88 they have shown that 
marked pulmonary invasion occurs constantly in hogs fed on 
tuberculous material. So also Ravenel 3 has recovered tu- 
bercle bacilli from the lungs within a few hours after placing 
them in the stomach by celiotomy. Beitzke 4 in a review of 
the subject states that Schlossmann and St. Engel 5 found the 
bacilli in the lungs six hours after injection into the stomach 
by laparotomy, as did also L. Rabinowitsch, and that the 
latter and also Uffenheimer, Bacharach, and Stein and Orth 
found them after injection into the intestine. Ficker, he says, 
could not do this with adult dogs or cats, and Herrmann could 
not with monkeys. Vallee, 6 Calmette and Guerin, 1 Bonome 7 
and Arloing 8 also have demonstrated pulmonary infection 

1 Calmette and Guerin, Ann. de l'lnst. Pasteur, 1905, XIX, 601; 
1906, XX, 353, 609. 

2 Schroeder and Cotton, U. S. Dept. Agric. Bu. An. Ind. Bull. No. 86 
and No. 93. 

3 Ravenel, Cleveland M. J., 1909, VIII, 179. 

4 Beitzke, Berl. klin. Wchnschr., 1908, XLV, 1235. 

5 Schlossmann and St. Engel, Deutsche med. Wchnschr., 1906, 
XXXII, 1070. 

6 Vallee, Ann. de l'Inst. Pasteur, 1905, XIX, 619. 

7 Bonome, Gazz. d. osp., Milano, 1907, XXVIII, Nos. 37-84, abstract 
in J. Am. M. Ass., Chicago, 1907, XLIX, 888. 

8 Arloing, Sixth Internat. Cong, on Tuberc, Wash., 1908, IV, 666. 



258 THE SOURCES AND MODES OF INFECTION 

via the alimentary tract, and very many of the experiments 
have shown that the bacilli easily pass through the intestinal 
wall without leaving a trace of their passage, so that the 
absence of lesion of the alimentary tract is no proof that 
infection has not taken place through it. 

Unnatural Conditions of Experiment. — Although there 
has been, as is here shown, a vast amount of experimental 
work on infection with tuberculosis, there has been very little 
in which the conditions at all approached the natural. Usu- 
ally there is an excessive amount of exposure, or an excessive 
number of germs in spray or dust. Thus in Cornet's nota- 
ble experiment, where 47 of 48 guinea pigs were infected by 
breathing dust, the carpet had been smeared with large 
quantities of sputum, and it was forcibly beaten so that 
clouds of dust rose up directly in front of the animals. It is 
surprising that so few have thought it worth while to see 
how infection takes place in animals kept under conditions 
as nearly as possible like those under which human beings 
live. 

Infection in Laboratory. — Animals kept in laboratories in 
company with others that have been purposely infected rarely 
contract the disease. Koch 1 in his original paper says that 
among the hundreds of animals so kept the disease did not 
develop for three or four months, and then only exception- 
ally. He reports autopsies on 17 guinea pigs and 8 rabbits 
thus naturally infected, which showed in all cases a pul- 
monary tuberculosis resembling that which occurs in man. 
But apparently no effort was made to determine whether 
infection was by the air, by the food, or by contact through 
the hands of attendants, though this laboratory infection has 
been urged as evidence that the disease is air-borne. Of many 
hundreds of guinea pigs confined in a room with various 
tuberculous animals in the Department of Agriculture Ex- 
periment Station at Washington, only one contracted tuber- 

1 Koch, Mit. a. d. k. Gesund.-Amt., 1884, II, Trans. Sydenham Soc. 
Pub., CXV, 129. 



INFECTION BY AIR 259 

culosis, and that was in a cage with several infected animals. 1 
In laboratories floating bacteria are not likely to be very nu- 
merous, owing to the cleanliness practiced and the fact that 
most of the laboratory animals do not excrete many bacilli. 
Experiments under Natural Conditions. Tuberculosis. — 
Schroeder and Cotton 2 experimented under more natural 
conditions. Seven cows were exposed in adjoining stalls to 
3 tuberculous animals, and all but 1 of them contracted the 
disease. As all but 2 were moved about from stall to stall, 
exchanging with the infected animals, infection may readily 
have been by contact. At the same time 100 guinea pigs 
were exposed in the stalls, one half in cages below the man- 
gers where food could sift through from the mangers, and 
one half on the walls. The exposure lasted several months, 
and only 1 of the pigs, in a cage under the manger, became 
infected. In a subsequent experiment 35 guinea pigs were ex- 
posed for one hundred and thirty-five days on the walls of 
the stalls. Two developed generalized tuberculosis. Of 42 
animals kept for fifty-one days under the manger of infected 
cows, 6 developed a more or less generalized type of the 
disease. There was no direct evidence that tubercle bacilli 
were in the air of the stalls, but as the infecting animals 
were excreting large numbers of bacilli, there is little doubt 
of it. There is no record that contact infection from the 
hands of attendants was strictly guarded against, and it may 
be that the 2 out of 135 guinea pigs, and the 2 cows supposed 
to have succumbed to air-borne infection, were really infected 
by contact. Swenson, quoted by Aufrecht, exposed five 
calves in a stable with tuberculous cows in such a manner as 
to preclude contact infection, and they all developed the 
disease, as Swenson thought, by dust infection. Klein 3 

1 U. S. Dept. Agric, Rep. Bu. An. Ind., Wash., 1906, XXIII, 31. 

2 Schroeder and Cotton, U. S. Dept. Agric., Rep. Bu. An. Ind., 
Wash., 1903, XX, 61; 1904, XXI, 44, reprinted as Circ. No. 83. 

• Stevenson and Murphy, Treatise on Hygiene and Public Health, 
Lond., 1893-96, II, 212, 



260 THE SOURCES AND MODES OF INFECTION 

exposed guinea pigs in the vent shaft of the Brompton Hos- 
pital, and most of them contracted tuberculosis. 

Experiments in Tuberculosis Houses. — Bartel and Spieler, 1 
realizing that most experiments are under unnatural con- 
ditions, exposed 12 guinea pigs in cages in a house occupied 
by tuberculous patients, and allowed 16 to run at large and 
be handled by the children. The exposure was from two to 
three weeks, and of the 12 cage pigs 3 developed tubercu- 
losis, and of the 16 free pigs 10 developed tuberculosis of 
various glands and other organs. No statement is made 
that care was taken to prevent contact or mouth-spray in- 
fection of the animals in the cages. These authors 2 exposed 
8 guinea pigs, running free, in a house where the tuberculous 
patient was taking fairly good care of the sputum. Only 1 
of the guinea pigs developed tuberculosis. 

At my suggestion Dr. M. S. Packard of Providence carried 
on an experiment for the health department of that city on 
the mode of infection of guinea pigs under natural conditions. 
A fairly clean laborer's house was chosen, where there was a 
consumptive whose sputum contained large numbers of ba- 
cilli, and who was taking no care whatever in regard to its 
disposal. Thirty-six small guinea pigs were exposed in cages 
placed in a dark place in the room in which the patient usually 
sat. The cages were much crowded. Of the animals, 16 
were fed and cared for by the consumptive, and the others 
by an employee of the department free from disease. These 
latter animals were locked in a box covered with wire net- 
ting, fourteen meshes to the inch. There could be no ques- 
tion of contact infection for these pigs. The exposure was 
from February 11, 1908, to May 14. All but 21 of the 
animals died of non-tuberculous disease, or were starved or 
killed by rats after removal from the house. Of the 11 
surviving animals exposed to air infection alone, 8 were 

1 Bartel and Spieler, Wien. klin. Wchnschr., 1905, XVIII, 218. 

2 Festschr. enthalt. Arb. u. Tuberk. ... VI Internat. Tuberk. Konf. 
[etc.], Wien u. Leipz., 1907, 71. 



INFECTION BY AIR 261 

shown to be tuberculous and 3 not tuberculous. Of the 
other lot, 7 were shown to be tuberculous and 3 not. It 
seems impossible that the test animals could have been in- 
fected otherwise than through the air. That it was mouth 
spray rather than dust infection seems likely, for the patient 
took much interest in the animals, and was often seen with 
his face close to the netting, talking to them, and coughing at 
them only a few inches distant. The guinea pigs were pur- 
chased, but I was unable to learn that they had ever been 
exposed to the disease. 

Since writing the above I note that Le Noir and Camus l 
have undertaken a similar experiment. The}- exposed guinea 
pigs in cages in a ward for phthisical patients. Four pigs 
were placed in a cage on the floor and the patients fed these. 
One of them developed tuberculosis. Five pigs were kept 
for six weeks in a cage on the floor but protected so that the 
patients could not reach them. One of these also developed 
tuberculosis. Another pig with three little ones was placed 
in a cage near the ceiling so that they had to be fed from a 
ladder. One of the little ones died of an intercurrent affec- 
tion, but the other two contracted tuberculosis. 

Since it is claimed by the majority of those interested in 
tuberculosis that the disease is spread chiefly by means of 
dust, it is highly desirable that a sufficient number of well- 
conducted experiments under truly natural conditions be 
made to determine how important this mode of infection 
really is. 

Except for tuberculosis very little animal experimentation 
has been done to determine whether diseases are air-borne. 
One reason for this, of course, is that so many of the com- 
moner diseases affecting human beings are not easily con- 
tagious for the lower animals. 

Experiments with Mediterranean Fever. — Horrocks, 2 
experimenting with monkeys, could cause Mediterranean 

1 Le Noir and Camus, Drome mod., Par., 1000, XVII, 761. 

2 Horrocks, Report of Royal Commission on Malta Fever. 



262 THE SOURCES AND MODES OF INFECTION 

fever by making the animals inhale dust artificially infected 
with large numbers of M . melitensis, but he was not successful 
with dust naturally infected with urine, though the organism 
of this disease is very resistant to drying. Monkeys kept in 
cages near infected animals did not contract the disease, 
unless there was actual contact with infected material, i.e., 
there was no air-borne infection. Epidemiological evidence 
is against this being a dust disease, for it prevails far less 
during the dry than during the wet season. That it is in 
reality exclusively milk-borne seems now to have been 
demonstrated. 

Experiments with Anthrax. — Buchner x was the first to 
attempt to infect animals by making them breathe dried 
anthrax bacilli or spores. He easily succeeded in thus caus- 
ing primary pulmonary disease. Miiskatbluth 2 showed that 
the spores would readily pass the lungs without causing local 
disease. Morse, Hildebrandt, Tschistovitsch and Gramat- 
schikoff 3 could not cause the disease by inhalation even 
when the spray was sent directly into the trachea. Baum- 
garten 4 believes that these various experiments show that 
infection takes place by the tonsils rather than directly by 
the lungs. 

Experiments with Plague. — Bubonic plague is often con- 
sidered an air-borne disease, but the experiments of the present 
Indian Plague Commission 5 have shown that this is not the 
case. Both monkeys and guinea pigs have in considerable 
numbers been put in flea-proof cages, but exposed freely to 
the air, and the cages placed in dwellings known to be in- 
fected, and in no instance did they contract the disease. In 
other instances the animals were exposed freely to the air, but 

1 Buchner, Centrlbl. f. Bakteriol. [etc.], Jena, 1890, VII, 733; 
VIII, 1. 

2 Miiskatbliith, Centrlbl. f. Bakteriol. [etc.], Jena, 1887, I, 321. 

3 Cited by Sobernheim in Kolle u. Wassermann Handbuch [etc.], 
Jena, 1903, II, 49. 

4 Lehrbuch der Pathologischen Mycologie, Braunschweig, 1890. 

6 Journal Hygiene, 1905, 835; 1906, 445-471; 1907, 432, 835, 979. 



INFECTION BY AIR 263 

were protected from fleas by " tangle-foot/' with like results. 
These experiments were made at various times and places, 
but the animals never succumbed to air-borne infection. In 
all instances control animals not protected from fleas usually 
contracted the disease. 

Conclusions. — After the foregoing survey of the subject 
we are, I think, justified in the following conclusions: 

1. The theory of the aerial transmission of disease was 
developed as the most reasonable way of explaining the phe- 
nomena of infection. 

2. Contact infection with carriers and missed cases affords 
a better explanation of the phenomena. 

3. The best medical thought has been steadily restricting 
the supposed sphere of aerial transmission. 

4. Only a few authorities now assert that disease is carried 
by the atmosphere outside of dwellings, and this assertion is 
made only in regard to smallpox. 

5. Bacteriology teaches that former ideas in regard to the 
manner in which diseases may be air-borne are entirely erro- 
neous; that most diseases are not likely to be dust-borne, 
and they are spray-borne only for two or three feet,*a phe- 
nomenon which after all resembles contact infection more 
than it does aerial infection as ordinarily understood. 
Tuberculosis is more likely to be air-borne than is any other 
common disease. 

6. Surgeons at first developed aseptic surgery on the theory 
that air infection was of the highest importance. They have 
gradually learned to pay less attention to it, until at present 
some of the best surgeons consider it a negligible factor. 

7. Animal experimentation indicates that tuberculosis and 
anthrax may be air-borne, and that plague and some other 
diseases are not. 

8. Pathology has not determined, as is sometimes alleged, 
that even pulmonary consumption is an air-borne disease. 

9. There is no good clinical evidence that the common 
diseases are air-borne. 



264 THE SOURCES AND MODES OF INFECTION 

10. There is considerable clinical evidence that scarlet 
fever, diphtheria, smallpox, measles, whooping cough, typhoid 
fever and plague are not easily transmissible through the air. 

11. Scarlet fever and diphtheria can be cared for in the 
same ward with other diseases without extension, if clean- 
liness be maintained and infection by contact avoided. 

In reviewing the subject of air infection it becomes evident 
that our knowledge is still far too scanty, and that the avail- 
able evidence is far from conclusive. Yet it is of the greatest 
practical importance that we should know definitely just what 
danger there is of air-borne infection and in what diseases 
it is to be feared. Infection by air, if it does take place, as is 
commonly believed, is so difficult to avoid or guard against, 
and so universal in its action, that it discourages effort to 
avoid other sources of danger. If the sick-room is filled with 
floating contagium, of what use is it to make much of an effort 
to guard against contact infection ? If it should prove, as I 
firmly believe, that contact infection is the chief way in which 
the contagious diseases spread, an exaggerated idea of the 
importance of air-borne infection is most mischievous. It is 
impossible, as I know from experience, to teach people to 
avoid contact infection while they are firmly convinced that 
the air is the chief vehicle of infection. 

While it is not possible at present to state with exactness 
the part played by aerial infection in the transmission of the 
different infectious diseases, we are by the evidence forced to 
the conclusion that the current ideas in regard to the impor- 
tance of infection by air are unwarranted. Without denying 
the possibility of such infection, it may be fairly affirmed 
that there is no evidence that it is an appreciable factor in 
the maintenance of most of our common contagious diseases. 
We are warranted, then, in discarding it as a working hy- 
pothesis and devoting our chief attention to the prevention 
of contact infection. It will be a great relief to most persons 
to be freed from the specter of infected air, a specter which 
has pursued the race from the time of Hippocrates, and we 



INFECTION BY AIR 265 

may rest assured that if people can as a consequence be 
better taught to practice strict personal cleanliness, they will 
be led to do that which will more than anything else prevent 
aerial infection also, if that should in the end be proved to be 
of more importance than now appears. 



CHAPTER VII. 

INFECTION BY FOOD AND DRINK. 

Infection by Water. 

Broad Street Well. — From time immemorial water has been 
believed to be the bearer of disease, but it is only since the 
middle of the nineteenth century that the subject has been 
scientifically studied. One of the first instances of a clear- 
cut demonstration of the causation of sickness by infected 
water was that of the now famous Broad Street well, so ably 
studied by Snow. 1 During the outbreak of cholera in Lon- 
don in 1854 there was an enormous concentration of cases 
in a very limited area just east of Regent Street, there having 
been reported, during a period of about six weeks, over 600 
fatal cases. A careful study of the site, soil, subsoil, streets, 
density and character of population, dwellings, yards, closets, 
cesspools, vaults, drains, conditions of cleanliness and atmos- 
pheric conditions, revealed nothing of interest. But a study 
of the water supply discovered most interesting facts. Nearly 
all of the cases were nearer a certain public pump in Broad 
Street than any other well, and most of them gave a definite 
history of getting water from this pump. Of the very few 
cases (ten at the time of the investigation) outside of the 
area supplied by this pump, half were known to drink water 
from Broad Street. There were also several cases of cholera 
in distant parts of London in persons who drank water from 
this well. In the workhouse with 535 inmates, in the midst 
of this district, but with its own well, there were only 5 
deaths, less than one-tenth the rate in the neighborhood, and 

1 Sedgwick, The Principles of Sanitary Science and the Public 
Health, New York, 1902, 170. 

266 



INFECTION BY FOOD AND DRINK 267 

in a brewery with 70 employees and using its own well there 
was not a single case. It was also shown that a privy vault 
and cesspool in the adjoining house discharged through a leaky 
drain which ran within two feet of the well. There were 4 
fatal cases of cholera in this house at the time of the outbreak 
and obscure earlier cases which were not unlikely cholera 
also. 

North Boston Well. — In the United States the outbreak 
of typhoid fever at North Boston, N. Y., in 1843, referred to 
by Flint in his popular text-books, did much to call attention 
to drinking water as a factor in the spread of disease. A 
young man from Massachusetts went to the hamlet sick with 
typhoid fever, and died there. He lodged at the tavern where 
there was a well of water used by 6 of the neighboring fam- 
ilies. One near-by family and 2 distant families did not 
use the water and had no illness. In the other families which 
did use the water there were 28 cases with 10 deaths. 1 

Recent Studies. — Such striking demonstration in a few 
instances of the spread # of disease through the medium of 
drinking water led to unwarranted generalization, and during 
the last half of the nineteenth century it was the common 
belief of health officials and medical men that infected water 
was the chief factor in the causation of typhoid fever and 
cholera, and that it was of great importance in malaria, yellow 
fever, dysentery, diarrhea, and was perhaps of moment in all 
the " zymotic " diseases. The discovery of the specific organ- 
isms of these diseases, and the application of more scientific 
methods to their study, has of late shown that water, while 
a factor of very great importance, is not so important as was 
at one time supposed. Let us consider its relation to specific 
diseases. 

Typhoid Outbreaks. — For dwellers in temperate regions 

typhoid fever is the most important water-borne disease. 

The demands of modern civilization require for the constantly 

increasing urban population a pipe-distributed municipal 

1 Am. Pub. Health Ass. Rep., 1873, I, 167. 



268 THE SOURCES AND MODES OF INFECTION 

supply which in numerous instances must be taken from 
streams or lakes more or less contaminated with sewage. 
The plentiful use of water rendered possible by a municipal 
supply produces a large amount of sewage, which in the past 
has usually discharged into the nearest watercourse, thus 
carrying danger to any other community which might become 
a user of the water. From what is known of the life history 
of the typhoid bacillus it is not surprising that in some cities 
great explosive outbreaks of the disease have been caused by 
a temporary pollution, and other cities, owing to continuous 
pollution of their source of supply, have suffered from a con- 
tinuous high death rate from this disease. The former class 
of outbreaks, while in the aggregate less destructive, are most 
impressive lessons for the public and have .been exceedingly 
instructive to the epidemiologist. The demonstration of a 
water-borne outbreak depends primarily upon statistics. If 
there is an excess of typhoid fever among the users of a certain 
water over the neighboring population living under the same 
conditions but using a different water, and if other sources, 
as food and milk, are excluded, the outbreak is probably 
water-borne. The more closely the users and non-users of 
the water are commingled, and the greater the difference in 
the incidence of the disease upon them, the more certain is the 
demonstration. During the outbreak in Scranton, 1 906-07, x 
there were four separate sections of the city not supplied 
from the infected reservoir in which there was very little 
typhoid, and most of the cases which did occur in these dis- 
tricts were shown to have used the infected water in other 
places, or to have been subject to contact infection. In 
Paris, 2 owing to partial failure of the good supply, the im- 
pure Seine water was turned on to one arrondissement after 
another, with the result that a well-defined epidemic followed 
in each instance. In Philadelphia the gradual introduc- 
tion of filtered water has resulted in a decrease in typhoid 

1 Wainwright, N. York M. J., 1907, LXXXV, 1027. 

2 Jordon, J. Am. M. Ass., Chicago, 1907, XLVIII, 1669. 



INFECTION BY FOOD AND DRINK 269 

fever, limited to those districts to which the water has been 
supplied. 

These water-borne outbreaks are usually explosive in char- 
acter and are frequently of short duration. An inspection of 
the supply not rarely shows that the feces of typhoid cases 
have entered the water shortly before the outbreak. Such 
outbreaks are apt to occur in the spring when the freshets 
wash the surface of the ground into the streams. The bacilli 
have rarely been found in the incriminated water. 

While studying this subject in 1888, 1 I was able to find 
thirteen recorded instances of the recovery of typhoid bacilli 
from water which had presumably been the cause of an out- 
break of the disease. In the outbreak in Providence in that 
year Prudden and Ernst reported finding the bacilli in house 
filters. Methods of identifying the bacillus at that time were, 
however, not entirely satisfactory, and it is not certain that 
the bacteria isolated were really typhoid bacilli. By better 
methods the germs have since been occasionally found in 
infected waters, 2 but as might be expected, it is more often 
from wells than from rivers or lakes. According to Got- 
schlich, 3 typhoid-fever germs have been identified in drinking 
water by the agglutination test only four times. Since then, 
however, they have been isolated by Wesbrook 4 from the 
Mississippi water at Minneapolis, and by Fox from the reser- 
voir which was the source of the Scranton outbreak. 5 The 
bacillus isolated by Wesbrook was used for years as a test 
organism in his laboratory and also by Harris at Johns Hop- 
kins. Anderson and Hutchings and Wheeler, as will be re- 
ferred to, determined the presence of typhoid bacilli in ice 
presumed to be the cause of the disease. 

1 Chapin, Boston M. & S. J., 1889, CXX, 604. 

2 J. Mass. Ass. Bds. Health, Bost., 1904, XIV, 66. 

s Gotschlich, Kolle u. Wassermann, Handbuch [etc.], Jena, 1903, 
I, 191. 

* Wesbrook, Brit. M. J., 1897, II, 1774. 
6 Rep. St. Bd. Health, Penn., 1907, 410. ' 



270 THE SOURCES AND MODES OF INFECTION 

Temporary Typhoid Infection. — These explosive and tem- 
porary outbreaks of typhoid fever among the users of muni- 
cipal supplies are sometimes due to an accidental pollution 
with sewage, but are more often due to the overflow of privies, 
or the placing of the discharges of typhoid patients on the 
ground where they can be washed into the streams. In our 
lake cities they have sometimes resulted from the wind tem- 
porarily blowing the sewage of the city towards the intake of 
the waterworks, 1 or the dumping of dredged mud near the 
intake. 2 Outbreaks are sometimes due to the careless tem- 
porary use of polluted water, owing to failure of the good 
supply, as at Newburyport, 3 or the accidental sucking in of 
polluted water owing to some derangement of valves or other 
mechanism, as in Lowell, 4 Baraboo and Millinocket. 5 

Continuous Typhoid Infection. — When considerable 
amounts of sewage are discharged into a stream or lake, the 
water, owing to the prevalence of typhoid fever, must be 
continuously charged with the bacilli. The users of the 
water under such circumstances generally suffer from a con- 
tinuously high death rate from this disease. Among cities 
which have so suffered may be mentioned Chicago, Pitts- 
burg, Cincinnati, St. Louis, Philadelphia, Newark and Al- 
bany. The unenviable position of many Pennsylvania cities 
in this respect is well set forth by Morris. 6 Among Euro- 
pean cities which have had a bad water supply are Berlin, 
Hamburg, Paris, Frankfurt, Altona, Breslau and Zurich. 
Under these circumstances the typhoid rate may, while re- 
maining high, vary considerably. Sometimes the incidence 
of the disease may reach enormous proportions, as in Chicago 

1 Whipple, Typhoid Fever, New York, 1908, 167-168. 

2 Whipple, Typhoid Fever, New York, 1908, 167; also U. S. Geol. 
Survey, Wash., Water Supply and Irrigation Papers, No. 194, 138. 

3 Rep. St. Bd. Health, Mass., 1892, 701. 

4 Whipple, Typhoid Fever, New York, 1908, 174. 

5 Whipple, Typhoid Fever, New York, 1908, 178-179. 

6 Morris, Sanitation, Phila., August, 1904, 47. 



INFECTION BY FOOD AND DRINK 271 

in 1891, when it was 173.8 per 100,000, and in Pittsburg in 
1900, when it was 144.2. Sometimes epidemic waves of the 
disease can be followed down a river from one municipal ity 
to another, as in the Merrimac, Kennebec and Hudson. 1 

Cities with Infected Water. — The connection between an 
excessive typhoid death rate and the sewage contamination 
of municipal water supplies is thus shown by a large amount 
of epidemiological evidence, but it is even more certainly dem- 
onstrated by the improvement which almost always follows 
when a pure water is substituted for the impure. Formerly 
typhoid fever was very common in English cities, but now 
the disease is far less prevalent, due in large measure to the 
almost universal use of clean water. Many continental cities 
present marked illustrations of the decrease in typhoid fever, 
due to improvement in water supply. Among such may be 
mentioned Paris, Berlin, Altona, Hamburg, Zurich, Breslau 
and Frankfurt. The United States also presents numerous 
examples, as Lawrence, Lowell, Albany, Buffalo, Newark, 
Jersey City, Cleveland, Chicago and Philadelphia. (For more 
detailed information see Whipple, " Typhoid Fever;" Fuertes, 
"Water and Public Health;" Hazen, "The Filtration of Public 
Water Supplies;" and Hazen, "Pure Water and How to Get 
It.") It has in one or two instances happened that the purifi- 
cation of a polluted water supply has not resulted in any very 
marked diminution in the typhoid death rate. This was so 
at Youngstown, Ohio, and notably at Washington. 2 At 
Youngstown the disease was shown to be spread chiefly by 
contact, or by the use of infected wells. The conditions at 
Washington are not so well understood, and a special com- 
mission 3 has been able to find no very definite cause for 
the disease. Levy and Freeman 4 after a very careful study 

1 Whipple, Typhoid Fever, New York, 1908, 149, 154, 236. 

2 Whipple, Typhoid Fever, New York, 1908, 248. 

3 U. S. Pub. Health & Mar. Hosp. Serv., Hyg. Lab., Bull. Nob. 35, 
44 and 51. 

* Levy and Freeman, Old Dominion J. M. & S., 1908, VII, 315. 



272 THE SOURCES AND MODES OF INFECTION 

of conditions in Washington and Richmond, conclude Aat 
Washington must be put in the category of southern cities 
in which an excessive typhoid-fever rate depends chiefly on 
climatic conditions operating more or less directly, and that 
perhaps to a considerable extent the disease depends on the 
presence of flies. However that may be, Washington affords 
a practically unique example among large cities of a mistake 
in attributing the excess of typhoid fever to the pollution of 
the water supply. 

Amount of Sickness Due to Water. — To how great an 
extent pollution of public water supplies is responsible for the 
excessive typhoid mortality in the United States it is difficult 
to determine. Whipple 1 says that the average typhoid death 
rate in American cities is about 35 per 100,000, while cities 
with a good water supply average not over 20. He would 
thus attribute to the pollution of public water supplies about 
40 per cent of the typhoid fever of the cities of the United 
States. We must remember, however, that an excess of 
typhoid fever in a city with a questionable water supply is 
not always due to the water, as witness Washington and 
Youngstown, and Dr. H. W. Hill writes me that Duluth is 
another example. But a majority of the people of this coun- 
try live beyond the reach of municipal water supplies, and 
typhoid fever is even more prevalent among this rural popu- 
lation. So that if the whole country is considered, it appears 
that 10 or 15 per cent, rather than 40 per cent, of our typhoid 
fever is the proper proportion to attribute to the infection of 
municipal supplies. 

Amount Due to Wells. — Doubtless the majority of the 
inhabitants of the United States obtain their drinking water 
from wells. Formerly polluted wells were believed to be the 
chief source of typhoid fever. This was particularly so while 
Murchison's "pythogenic" theory of the origin of the disease 
prevailed. When wells were a principal source of supply in 
cities where privy vaults and cesspools abounded, probably 
1 Whipple, Typhoid Fever, New York, 1908, 132. 



INFECTION BY FOOD AND DRINK 273 

they were often the source of typhoid fever. With the sub- 
stitution of municipal pipe-supplies, the well has become a 
factor of comparatively little moment in city typhoid fever. 
As it now appears that the bacillus of this disease does not 
survive long in soil or water, and that each case must have 
some connection with a previous case of human typhoid 
infection, it seems improbable that country wells, largely iso- 
lated as they must be from danger of indiscriminate human 
contamination, play an important part in the propagation of 
the disease. This is the view held by Hill, who has had a 
large experience in the study of this disease in Minnesota. 
He states, however, that sometimes in loose coarse gravel, 
or in seamy shale and limestone formations, wells may become 
infected from sources of pollution situated at long distances, 
and have then been known to be the cause of much sickness. 
Instances of Infected Wells. — That wells have actually 
been the source of typhoid fever there is much evidence. 
Instances of outbreaks due to infected wells at Basingstoke, 
England, Newport, R. I., and Trenton are narrated by Whip- 
ple, 1 and a dozen or more instances in England are referred to 
by Poore, 2 and some of the 179 milk outbreaks of typhoid 
fever tabulated in " Milk and Its Relation to the Public 
Health" 3 were due to infection of the milk by water from a 
contaminated well. Outbreaks due to well water continue 
to be reported from time to time. During twenty-five years 
no instance of typhoid fever from infected well water has 
come under my personal notice except at a summer hotel on 
the shore of the bay, in which case the well was probably 
infected by a broken drainpipe near by. An interesting case 
was noted in Washington a few years since. 4 Typhoid fever 
occurred in four houses on a certain street, all supplied from 

1 Whipple, Typhoid Fever, New York, 1908, 183-188. 

2 Poore, The Earth in Relation to the Preservation and Destruc- 
tion of Bacteria, Lond., 1902, 135. 

8 U.S. Pub. Health & Mar. Hosp. Serv., Hyg.Lab. Hull. Xo.41,50. 
' District of Columbia, Report of Health Officer, 1903, 29. 



274 THE SOURCES AND MODES OF INFECTION 

wells. A little further up the street there had previously 
been some cases, the feces from which had been thrown into 
a privy box after what was probably only partial disinfection 
with carbolic acid. At any rate carbolic acid could be tasted 
in the water in the wells below. While in this instance the 
infecting material probably percolated through the soil, as 
it did also in the outbreak at Trenton, Whipple states: 1 
" Sandy soil is a good filtering material, and when a well in 
such soil stands at the center of a circle twenty-five or fifty 
feet in radius in which there are no privies, cesspools, sink 
wastes, or other sources of contamination, the water can 
usually be depended upon as fit for domestic use, — provided, 
of course, that the top of the well is properly guarded against 
surface wash." Sometimes, as in the Trenton incident, the 
infecting material passes a considerable distance apparently 
through channels or crevices. The writer once knew of a well 
which became polluted (though without causing sickness) 
from a privy 300 feet distant, after there had been much 
blasting near by, which presumably opened seams in the 
somewhat slaty rock. As Whipple says, most wells which 
have been the cause of typhoid outbreaks have been contam- 
inated from the top. 

Infected Springs. — Springs are essentially natural wells, 
and there is no reason why they should not occasionally be 
contaminated. A typhoid outbreak caused by spring water 
occurred at Mount Savage, Md., in 1904, 2 another at Spring- 
field, Mass., 3 one at Northampton, Mass., 4 one at Ridgway, 
Penn., 5 and two others in Maryland. 6 

Typhoid Fever from Bathing. — It has been suggested 
from time to time that typhoid fever may result from bathing 

1 Whipple, Typhoid Fever, New York, 1908, 85. 

2 Whipple, Typhoid Fever, New York, 1908, ]88. 

3 Rep. Bd. Health, Springfield, 1903, 16. 

4 Rep. St. Bd. Health, Mass., 1900, 844. 

5 Rep. St. Bd. Health, Penn., 1907, 927. 

6 J. Am. M. Ass., Chicago, 1905, XL1V, 595. 



INFECTION BY FOOD AND DRINK 275 

in water containing typhoid bacilli, the infection presumably 
being due to the accidental swallowing of some of the water. 
Reece ' has recently reported an outbreak, presumably due 
to this cause, at the naval recruiting station at Walmer. The 
swimming tank was infected with sewage containing typhoid 
excreta, and the earlier cases seemed to be closely connected 
with the use of the tank. From the report, however, it does 
not appear that contact infection outside the tank could be 
rigidly excluded. 

Cholera from Water. — Cholera was early shown to be 
a water-borne disease. The longevity of the spirillum in 
water is probably not so great as that of the typhoid bacillus, 
but it is sufficient to permit of the disease being easily trans- 
mitted in this manner. Whenever the excreta of human 
beings infected with cholera gain access to cisterns, wells, 
streams or other sources of drinking water, cholera is pretty sure 
to follow. The cholera-infected Broad Street well in London 
has been referred to, and although for many years the views 
of health officials were somewhat colored by the miasm theory 
of Pettenkofer, the transmission of the disease by water was 
kept in mind, and many outbreaks due to this cause were 
reported. Radcliffe, Simon and others 2 showed that infected 
water played a large part in the outbreaks of cholera in Lon- 
don in 1848-49, 1853-54 and 1866. Shakespeare in his very 
valuable Report on Cholera in Europe and India 3 gives nu- 
merous instances of water-borne cholera infection, as from 
wells at several places in France (pp. 76-81), and from muni- 
cipal supplies in Genoa and Naples (p. 151). In Spain many 
towns and villages suffered from water-borne outbreaks, 
caused often, doubtless, by the universal custom of washing 
soiled linen in running streams. According to Shakespeare, 
water plays an important part in the spread of cholera in 

1 Rep. Med. Off. Loc. Gov. Bd., 1908-09, XXXVIII, 90. 
1 Sedgwick, Principles of Sanitary Science and the Public Health, 
New York, 1902, 182. 

» U. S. Government Printing Office, 1890. 



276 THE SOURCES AND MODES OF INFECTION 

India, and Koch 1 reported finding the spirilla in a tank used 
as a village water supply. A number of instances of the 
finding of cholera spirilla in water that was presumably the 
cause of the disease are noted by Kolle. 2 Cases are recorded 
of explosive outbreaks of cholera on shipboard, probably due 
to infected water. 3 The most striking instance of the trans- 
mission of cholera by water is the celebrated outbreak in 
Hamburg and Altona in 1892. These two municipalities 
form practically one city, though each has its own water 
supply. In the outbreak Hamburg, which used unfiltered 
and polluted Elbe water, suffered severely, while Altona, the 
water for which was filtered, was almost exempt. The line of 
demarcation between the two water supplies could be recog- 
nized by the incidence of the disease. Our officers in the 
Philippines attribute great importance to water as a vehicle 
for the diffusion of cholera, particularly in the villages and 
smaller towns, where the streams are used for washing clothes 
and for sewers and at the same time as sources of domestic 
supply. The municipal supply of Manila has been kept free 
from infection during the last outbreaks, though wells have 
to some extent been the cause of sickness. Woodruff 4 states 
that in one town a spring supplied part of the people, who 
were quite free from the disease, which nearly decimated those 
using the river, and in those towns where the people had well- 
protected rain-water cisterns they were quite immune. While 
we are not in a position to determine the relative importance 
of water in the causation of cholera, it appears certain that it 
is a factor of great consequence, and that people using a 
sewage-polluted water are, on the advent of cholera, liable to 
suffer from severe epidemics of the disease. 

Dysentery from Water. — The bacillus of dysentery is found 
in the discharges from the bowels, and has about the same 

1 Koch, Brit. M. J., Lond., 1884, II, 403, 453. 

2 Kolle u. Wassermaim, Handbuch [etc.], Jena, I, 191; III, 61. 

3 Wendt, Asiatic Cholera, New York, 1885, 113. 

4 Woodruff, J. Am. M. Ass., 1905, XLV, 1160. 



INFECTION BY FOOD AND DRINK 277 

resistance as the typhoid bacillus, so that we should expect 
this form of dysentery to spread in much the same way as 
typhoid fever does, and that infected water would prove a 
factor of importance. Shiga 1 reports outbreaks in Japan from 
the use of well and river water. Eldridge 2 states that dysen- 
tery is a rural disease in Japan, and the use of human feces 
as a fertilizer, and the frequency of the infection of the nu- 
merous small streams and wells, renders it preeminently a 
water-borne disease. 

The causative agent of amebic dysentery, according to 
Musgrave and Clegg, grows outside of the body in soil and 
on various vegetables. It is therefore likely to be trans- 
mitted by water, and indeed was recovered by Musgrave and 
Clegg 3 from 17 of 61 samples of the public water supply of 
Manila, and was found in tanks used for holding distilled 
water, and also in many wells. Recently Allan 4 has re- 
ported a small outbreak of amebic dysentery in North Caro- 
lina, due to an infected well. 

Diarrhea from Water. — Diarrhea has been thought by some 
to be due to the infection of drinking water. Thus Reincke 5 
states that infantile diarrhea was greatly lessened after the 
improvement in the water supply of Hamburg. Sir Shirley 
F. Murphy, Seaton and Newsholme in the discussion of the 
paper took issue with its writer as to the part played by 
water in the causation of this disease. Sedgwick 6 says that 
there is no doubt that drinking water is the ready vehicle of 
dysentery and diarrhea. He refers to the Ninth Report of 
the Medical Officer of the Privy Council, London, 1867, p. 16, 

1 Shiga, Mod. Med. [Osier], Phila. & X. Y., 1907, II, 781. 

2 Eldridge, U. S. Pub. Health & Mar. Hosp. Serv., Pub. Health 
Rep., 1900, 1. 

3 Musgrave and Clegg, Bull. 18 Bu. Gov. Lab., P. I., 93; Rep. Bd. 
Health, P. I., 1904-05, 10. 

* Allan, J. Am. M. Ass., Chicago, 1909, LIII, 1561. 

5 Reincke, Trans. Epidemiol. iSoc, Lond., 1904, n. s., XXIII, 135. 

6 Sedgwick, Principles of Sanitary Science and the Public Health, 
New York, 1902, 217. 



278 THE SOURCES AND MODES OF INFECTION 

and to his own investigations as to the excessive prevalence of 
typhoid fever and diarrhea in Burlington owing to the sewage 
contamination of the water supply. 1 In Albany 2 there was 
a reduction of 57 per cent in the mortality from diarrheal 
diseases after the introduction of filtration in 1898. Such 
statistical evidence does not seem to the writer to be of much 
value, and the evidence elsewhere given of the part played by 
milk and contact indicates that it is improbable that water 
has much influence in the causation of diarrheal diseases. 

Malaria from Water. — Until recently malaria has been 
believed to be transmitted by means of drinking water. 
Numerous instances were reported, such as that of the ship 
Argo, in which it was supposed that the evidence pointed 
conclusively to this mode of transmission. The discovery of 
the part played by the mosquito in the causation of this 
disease led to a more critical consideration of the alleged 
evidence in support of its water-borne character, and most 
of this evidence was found to be worthless, or in the few 
instances in which water still seemed to be at fault it appeared 
probable that the water served as .a breeding place for mosqui- 
toes, and did not directly cause disease by its ingestion. 

There was nothing in the earlier demonstrated facts of the 
transmission of the disease by insects to preclude the pos- 
sibility of its transmission by water, and indeed Laveran and 
Manson thought this not improbable. Celli 3 attempted to 
demonstrate this in various ways by administering water 
from the most malarious regions of Italy to human beings, 
daily, up to a month. He failed completely, as, according to 
Craig, 4 have all other experimenters, except Ross in one in- 
stance, which, however, from the conditions of the experiment 
was far from conclusive. Celli considers the fact that large 
numbers of railway employees and others living in intensely 

1 J. N. Eng. Water Works Ass., X, 167. 

2 Whipple, Typhoid Fever, New York, 1908, 276. 

3 Celli, Malaria, Lond., 1900, 94. 

4 Craig, The Malarial Fevers, New York, 1909, 82. 



IXFECTIOX BY FOOD AXD DRIXK 279 

malarious regions around Rome use an unquestionably pure 
aqueduct water, but are yet frequently attacked by malaria, 
is corroborative evidence that water cannot be an important 
vehicle of the disease. But probably the best evidence we 
have that drinking water plays no part in the causation of 
malaria is the fact that preventive measures all over the 
world, directed solely against the mosquito and with no ref- 
erence to the water theory, have resulted in an enormous de- 
crease and in some places in the eradication of the disease. 

Yellow Fever from Water. — Yellow fever also was formerly 
believed to be at times water-borne, but as in malaria the 
epidemiological evidence therefor will not stand criticism. 
The success of the preventive measures directed solely 
against the mosquito indicates that drinking water has no 
part in the diffusion of this disease. 

Tuberculosis from Water. — Dixon and Fox l showed that 
tubercle bacilli may be recovered from sewage, as might have 
been suspected from what is known of the biology of the or- 
ganism. It must be frequently swallowed by human beings, 
and, as in cattle, is likely to be voided in a living state in the 
feces. The washings of pastures and stables must also carry 
the bovine form of the bacillus in considerable numbers into 
waters which are quite free from pollution by human excreta. 

Hazen has attempted to show that the purification of 
sewage-contaminated public water supplies decreases the 
general death rate of a city, as well as the typhoid mortality. 
Thus it was stated that the use of niters on the Albany water 
supply caused a decrease in deaths from malaria, diarrheal 
diseases and also a general decrease in the deaths of children 
under five years of age. During a study of this claim of 
Hazen's, that the purification of a polluted water supply 
results in a marked decrease in the general mortality, Sedg- 
wick and MacXutt 2 came to the conclusion that among the 
diseases thus affected pulmonary tuberculosis holds an im- 

1 Dixon and Fox, J. Am. M. Ass., Chicago, 1908, LI, 380. 

2 Sedgwick and MacXutt, Science, X. Y., 1908, n. s., XXVIII, 215. 



280 THE SOURCES AND MODES OF INFECTION 

portant place. These writers compared the phthisis death 
curve in Lowell and Lawrence, two cities which some years 
since substituted pure for impure water, with the curve for 
the same disease in Manchester, another and near-by city 
with a similar population and business, which for a long 
time had had a pure and unchanged public water supply. 
During the five-year periods considered the phthisis death 
rate in Lowell fell 83 per 100,000 living, and in Lawrence 59, 
while Manchester showed a decrease of only 5 and 30 for the 
same periods. (The improvement in the water supply of Lowell 
and of Lawrence was not made at the same time.) The total 
death rate, and particularly the death rate from pulmonary 
tuberculosis, has been falling very generally of late, and the 
gross death rate, and even that for a single disease like tuber- 
culosis, is determined by a very large number of factors. To 
draw such far-reaching conclusions from a study of only three 
cities seems somewhat dangerous, and I would much prefer 
to consider the question still open as to whether the incidence 
of pulmonary tuberculosis is affected by the water supply. 
The above-named writers come to no conclusion as to whether 
the decrease in the death rate from tuberculosis is due to 
decrease in infection or improvement in resistance. Sedg- 
wick and MacNutt also believe that the death rate from 
pneumonia is affected by the water supply. 

Worms in Water. — The eggs and young of some of the 
parasitic worms are often swallowed in drinking water, and 
the Ankylostoma and Bilharzia, and others probably, enter 
the skin from water in which they are contained, but the 
consideration of the diseases caused by them is outside the 
scope of this essay. 

Conclusions. — Among the common infectious diseases, 
typhoid fever is practically the only one at present of any great 
importance to the people of Western Europe and North 
America which is often disseminated by means of drinking 
water. It is probably true that dysentery also may be spread 
in the same way, but it does not at present appear to be very 



INFECTION BY FOOD AND DRINK 281 

common, or to occur often in water-borne outbreaks. Asiatic 
cholera too may cause great devastation through infection of 
water supplies, but for a number of years the western world 
has been remarkably free from this disease. Typhoid fever 
is, however, such a common and serious disease, causing prob- 
ably 25,000 deaths annually in the United States, as well as 
an enormous amount of disability at the most useful period 
of life, that it is worth while to make large expenditures for 
its prevention. Such expenditures are to be still further 
encouraged, since it is certain that the means taken to pre- 
vent the diffusion of typhoid fever by water will also prevent 
the spread of cholera and bacillary dysentery. 

Protection of Water Supplies. — In the three diseases just 
mentioned the sole source of infection of water is the excreta 
of persons infected with the specific germs. If these excreta 
can be kept out of drinking water, or if the germs can be 
removed from it after it is infected, the problem is solved, and 
this can be done at a not prohibitive expense. For a full 
and practical consideration of the means for obtaining a pure 
water supply reference should be had to such works as Hazen's 
" The Filtration of Public Water Supplies" and "Pure Water 
and How to Get It." Suffice it to say here that pure water 
may be obtained by securing a clean source or by adopting 
some method of purification. 

Domestic Wells. — The larger part of our population ob- 
tains its drinking water from shallow wells, and it is usually 
neither difficult nor expensive so to locate them that they 
will not receive drainage from privies or sink drains, and so 
to protect them that they will not receive surface washings. 
The federal Department of Agriculture and the state and local 
boards of health should do and are doing much to instruct 
farmers and villagers concerning the location and protection 
of wells. 

Municipal Supplies. — As regards municipal supplies it is 
desirable if possible that the water be uncontaminated. This 
may be secured by drawing from deep wells, or seeking a 



282 THE SOURCES AND MODES OF INFECTION 

source in a sparsely inhabited region. Some cities, as Liver- 
pool, Boston and New York, have spent large sums to bring 
clean water from long distances. Other cities, notably Chi- 
cago, have secured good water by the construction of expen- 
sive works to remove sewage from the watershed. Many 
cities, when there is only a limited danger of pollution, ac- 
complish much by a continuous patrol of the watershed 
and the removal of minor sources of pollution under general 
or special nuisance laws. In many states this duty of pro- 
tection has been laid upon the state boards of health, and 
in some instances cooperation between states becomes 
necessary. 

Purification of Water. — Unfortunately it often happens 
that it is physically impossible for a municipality to obtain 
a sufficient supply of water which is not subject to dangerous 
pollution. Purification then becomes a necessity, and owing 
to the labors of a long line of chemists, engineers and bacteri- 
ologists, several efficient and economical methods for accom- 
plishing this have been developed. First among these is 
filtration. There are various methods of filtration, applica- 
ble to different waters and different localities, and it is the 
business of specialists to devise the best system for each city 
confronted by the problem. Efficient filtration will remove 
over 99 per cent of the contained bacteria, but cannot be relied 
upon to remove amebse. Hence filtration will not protect 
against amebic dysentery, but it will protect against the 
bacillary form and against typhoid fever and cholera. That 
it is efficient against typhoid fever is shown by the experience 
of London, Berlin, Zurich, Hamburg, Lawrence, Albany, 
Paterson, Philadelphia and many other cities, and the re- 
moval of cholera spirilla was beautifully shown by the ex- 
perience of Altona in 1893. The storage of water rapidly 
removes bacteria by sedimentation and through the death of 
the organisms, and is often a useful adjunct to filtration, 
notably so in the case of some of the London water companies. 
The boiling of water is an effectual means of destroying dan- 



INFECTION BY FOOD AND DRINK 283 

gerous bacteria, and as a domestic measure it is sometimes 
extremely useful. 

The use of hypochlorite of lime (commercial bleaching 
powder) has within a short time come into use for the pur- 
pose of sterilizing municipal water supplies. While this 
method of protection had been used in England as a tem- 
porary expedient, its first use as a permanent method of 
treatment seems to have been by Leal, at Boonton, N. J., 
in 1908. 1 A high degree of safety seems to be secured at a 
low cost. The subject has been investigated also by Clark 
and Gage, 2 Phelps, Park, Pratt and others. The process has 
been used at East Providence, R. I., Poughkeepsie, Chicago 
and other places. 3 

Infection by Ice. 

Danger Exaggerated. — The use of ice from polluted 
sources has always been viewed with some alarm, and when 
it became known from the work of Prudden 4 and others that 
the bacilli of typhoid fever live for some months when frozen 
into ice, the alarm was believed to be well founded. But 
further researches (see page 10) have shown that in the 
freezing of ice under normal conditions a large proportion 
of the bacteria in the ice are frozen out, and those that remain 
tend to die off quite rapidly, somewhat as they do in water. 
Hence theoretically little danger is to be apprehended from 
the use of ice cut from water considerably polluted, even 
so polluted that if the water itself were used it would 
probably cause disease. There is very little epidemiological 
evidence that ice has been the cause of sickness. The litera- 
ture relating to the subject was collected by Sedgwick and 

1 Leal, Fuller, Johnson, Papers read at the 20th Annual Con- 
vention of the American Water Works Association, 1909. 

2 J. N. Eng. Water Works Ass., 1909, XXII, 302. 

3 Discussion of a paper by Phelps at a recent meeting of the Boston 
Society of Civil Engineers, Abst. Eng. Rec, 1910, XLI, 80. 

* Prudden, Med. Rec, N. Y., 1887, XXXI, 341. 



284 THE SOURCES AND MODES OF INFECTION 

Winslow l in 1902. An outbreak the exact nature of which 
was not determined occurred at Rye Beach, N. H., in 1875, 
due presumably to the use of ice from a pond grossly polluted 
with decaying vegetable matter. A single case of typhoid fever 
in Connecticut appeared to be due to the use of specifically 
infected ice. Alleged outbreaks of typhoid fever and dysen- 
tery in the United States, and of typhoid fever in Evesham, 
England, and Rennes, France, were also noted by the above- 
named authors, but the evidence was far from conclusive. 
More recently Hutchings and Wheeler 2 report an outbreak 
of typhoid fever in a hospital at Ogdensburg, N. Y. Eight 
persons were attacked, and the disease seemed to be due to 
the use of ice. An examination of the ice in the ice house 
showed that some of it contained visible dirt from which 
colon and typhoid bacilli were isolated. Anderson 3 reports 
an outbreak at Lexington, Va., possibly due to artificial ice 
made from spring water polluted with typhoid excreta, from 
which water he isolated typhoid bacilli, proved to be such 
by cultural and agglutination tests. Hamer 4 refers to a pos- 
sible instance of ice-borne typhoid in London in 1898. Judg- 
ing from the small number and indefinite character of these 
reports, it appears that there is little direct evidence that ice 
is a factor of any moment in the diffusion of the contagious 
diseases. On the other hand there is strong epidemiological 
evidence that it is not, and this is in accord with the bac- 
teriological findings. Hundreds of thousands of tons of ice 
are cut from sewage-polluted waters in the United States, 
but sickness does not appear to follow the use of this ice in 
drinking water. Park 5 has studied this point in New York 
City, where four-fifths of the ice is cut from the markedly 

1 Sedgwick and Winslow, Mem. Am. Acad. Arts & Sc., 1902, XII, 
No. 5, 472. 

2 Hutchings and Wheeler, Am. J. M. Sc, Phila., 1903, n. s., CXXVI, 
680. 

3 Anderson, Med. Rec, N. Y., 1908, LXXIV, 909. 

4 Hamer, Rep. Med. Off. Health, Lond., 1904, Appendix I. 
6 Park, J. Am. M. Ass., Chicago, 1907, XLIX, 731. 



INFECTION BY FOOD AND DRINK 285 

contaminated Hudson River. Vast quantities of this ice are 
used in drinking water, and if it is the bearer of typhoid 
fever there should begin a noticeable increase of the disease 
when the use of the new ice commences in March, and this 
increase should continue during April and May. During the 
ten years studied by Park no such increase was noted, and 
no outbreak occurred which could be attributed to ice. 

Infection by Milk. 

Character of Outbreaks. — It has long been known that 
some of the common contagious diseases of human beings 
may be transmitted by means of milk. The only diseases 
that are definitely known to be so carried are typhoid fever, 
scarlet fever and diphtheria. There is no reason why dysen- 
tery and cholera, and perhaps other diseases, should not be 
transmitted in the same way, but no evidence of it has come 
to my knowledge, except that referred to by Kober, 1 who 
states that McNamara in Calcutta, in 1872, traced an out- 
break of cholera to an infected dairy. Outbreaks of the 
above diseases have been reported from time to time, and 
have been studied by Hart, Kober and others, but the latest 
tabulation and the fullest consideration of the subject are 
to be found in Bulletin 56, Hygienic Laboratory, United 
States Public Health and Marine Hospital Service, 1909. 
Milk outbreaks of these diseases have an explosive character, 
such as is shown by water-borne outbreaks of typhoid fever. 
In scarlet fever and diphtheria the explosive character is owing 
to the shorter incubation of these diseases, more pronounced 
than it is in typhoid fever. A milk outbreak is determined 
to be such from the presence of an excessive number of cases 
on a particular milk supply which cannot be accounted for 
in any other way. From three to five cases within a few 
days on a route covered by one wagon in a city with an 
average typhoid death rate is highly suspicious, and in most 

1 Kober, J. Am. M. Ass., Chicago, 1907, XLIX, 1091. 



286 THE SOURCES AND MODES OF INFECTION 

instances proves to be the beginning of an outbreak. The 
more the customers of a dealer are scattered, the stronger 
is the evidence. Care must be taken to exclude all other 
sources, such as neighborhood or family contact, water, ice, 
shellfish or other foods. Milk outbreaks often prevail more 
extensively among the well-to-do, owing to their greater con- 
sumption of milk, and a typhoid milk outbreak usually shows 
a high percentage of children attacked. Often the source of 
infection can be found. In only two instances reported by 
Konradi l and Shoemaker 2 has the typhoid bacillus been 
isolated from milk, and in only four instances has the 
diphtheria bacillus been recovered. 3 

Number of Outbreaks. — The number of outbreaks pretty 
definitely traced to milk is quite large. Trask, in the Hygi- 
enic Laboratory Bulletin referred to, tabulated 179 outbreaks 
of typhoid fever, 51 of scarlet fever, 23 of diphtheria and 
7 of sore throat. Besides these Hart reported 51 of typhoid 
fever, and Busey and Kober 86 of typhoid fever, 59 of scarlet 
fever, 21 of diphtheria, making in all 316 outbreaks of typhoid 
fever, 125 of scarlet fever, 51 of diphtheria and 7 of sore 
throat. In these are not included the 90 outbreaks tabu- 
lated by Caroe. This is certainly an impressive aggregate, 
but it must be remembered that these records cover a period 
of perhaps half a century. To determine within any degree 
of accuracy how large a part milk plays in the spread of 
these diseases is difficult, but it seems to me that the tend- 
ency at the present time is to exaggerate its importance. 
Schuder 4 found that of 640 outbreaks of typhoid fever 462 
were caused by water and 110 by milk, but it is highly im- 
probable that cases caused respectively by water and by milk 

1 Konradi, Centralbl. f. Bakteriol. [etc.], Jena, I Abt. Orig., XL, 31. 

2 Shoemaker, J. Am. M. Ass., Chicago, 1907, XLVIII, 1748. 

3 Nuttall and Graham-Smith, The Bacteriology of Diphtheria, 
Cambridge, 1908, 326. 

4 Schuder, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1901, 
XXXVIII, 343. 



INFECTION BY FOOD AND DRINK 287 

occur in any such ratio in the United States. Most of the 
water-borne typhoid fever does not occur in outbreaks, but 
is due to the continuous pollution of municipal supplies. 
Milk-borne typhoid fever, on the other hand, probably does 
occur chiefly in the form of outbreaks. During the last four 
years, in Providence, 155 of the 600 milk dealers have had 
one or more cases of typhoid fever on their routes. In only 
9 instances have there been more than 2 cases on a single 
route within a week. Investigation promptly showed that 
in 3 instances the groups of cases were due to personal con- 
tact, and in the other 6 instances an unmistakable milk 
outbreak developed. It is true that some epidemiologists 
assume that a considerable number of sporadic cases are due 
to milk, but the evidence appears to be the other way. I 
think that a study of the distribution of typhoid cases on 
milk routes in Washington, as shown in diagrams in bulletins 
35, 44 and 52 of the Hygienic Laboratory, United States 
Public Health and Marine Hospital Service, bears out my 
contention that outbreaks of typhoid fever due to milk are 
not likely to escape notice if the cases are daily tabulated 
according to milk supply. Furthermore, these charts show 
that there is little excess of typhoid fever on individual milk 
supplies except in those instances where there is a noticeable 
outbreak. 

Fewer Outbreaks in Large Cities. — It is also to be noted 
that verj T few outbreaks are reported from the large cities 
like New York, Chicago and Philadelphia, due perhaps to 
the fact that the chemical and bacteriological changes in the 
milk resulting from the long haul necessary for such cities 
are unfavorable for the typhoid bacillus. In the country, 
milk outbreaks are not likely to be a factor of moment, as 
large milk routes are not common. It is in the medium- 
and smaller cities and villages that most of the milk out- 
breaks are reported. It will be noted that though Boor 
outbreaks of typhoid fever may occur each year, they do not 
include more than a small fraction of the total typhoid fever. 



288 THE SOURCES AND MODES OF INFECTION 

It may be claimed that only a small proportion of the milk- 
borne outbreaks are recognized as such, but I cannot think 
that this is so in the English cities and the better class of 
American cities. In Providence during the last twenty-five 
years there have been nine outbreaks of typhoid fever, includ- 
ing 363 cases, or about 8 per cent of the total occurring during 
that time. But the typhoid death rate in Providence is 
below the average, so that 8 per cent in Providence would 
probably be equivalent to not over 4 per cent in the average 
American city with its polluted water supply and numerous 
privy vaults. In only a few cities have Trask, Hart, and Busey 
and Kober been able to find records of more than two, or more 
rarely three, outbreaks ; yet we can scarcely believe that milk 
outbreaks could have, except rarely, escaped detection in the 
English cities, or in such cities as Boston, Worcester, Spring- 
field, Rochester, Baltimore, Philadelphia and New York. 

Amount of Typhoid Fever Due to Milk. — The city of 
Washington is reported as showing an excessive amount of 
milk-borne typhoid fever. 1 In 1906, 79, or 9 per cent, of the 
866 cases investigated by the commission, were traced to milk; 
in 1907, 31, or 5 per cent, of 635 cases investigated; and in 
1908, 54, or 8 per cent, of 679 cases. According to figures 
furnished by Dr. Woodward, Health Officer of Washington, 
the number of typhoid cases due to milk during the three 
years was 139, which gives a percentage of 4.6. The com- 
mission considers that 10 per cent of the typhoid fever in 
Washington is due to milk. These percentages, however, seem 
to me unfair, as doubtless all the outbreaks were reported, 
and the percentages should, from the standpoint of the present 
consideration, be based on the total number of cases reported 
in the city, and not on the cases studied and of known origin. 
This gives a percentage, as above stated, of 4.6 of the typhoid 
fever in Washington during the three years 1906-08 as due 
to milk-borne typhoid. The importance and value of the 

1 U. S. Pub. Health & Mar. Hosp. Serv., Hyg. Lab., Bull. No. 35, 
59; No. 44, 46; No. 52, 100. 



INFECTION BY FOOD AND DRINK 289 

reports on typhoid fever in Washington have, as it appears, 
given a rather exaggerated importance to the danger from 
milk. That there was a certain amount of typhoid fever in 
Washington due to milk, during the three years in question, is 
no reason for assuming a similar percentage of milk-borne 
typhoid fever for the other cities of the country. Trask was 
able to find during the years 1903-07 about 1900 cases in 
the United States traced to milk. During this period there 
were in the registration area 57,023 deaths, and the total num- 
ber in the whole country must have been at least double, or 
114,000. The fatality is probably not over 10 per cent, so 
that there must have been at least 1,000,000 cases. Nine- 
teen hundred is 0.19 per cent, which is very different from the 
10 per cent now commonly assumed as due to milk. I do not 
of course believe that all the milk outbreaks were reported, 
but the number would have to be increased fifty-fold to 
equal 10 per cent, and it can scarcely bfe believed that 98 per 
cent of all milk outbreaks fail of recognition. 

Scarlet Fever and Diphtheria. — Scarlet fever and diph- 
theria are certainly much more rarely transmitted by means 
of milk than is typhoid fever. Although the percentage of 
typhoid fever, scarlet fever and diphtheria due to milk is 
small, the danger is a real one and the aggregate of cases not 
inconsiderable, and their occurrence should, if possible, be 
guarded against. 

Animal Sources. — The infection of milk with the above 
diseases is almost invariably from human sources. There is 
no evidence to show that cows may be infected with the 
bacillus of typhoid fever, and the contamination of the milk 
by drinking sewage-polluted water does not occur. Scarlet 
fever also does not appear to be an animal disease. Power 
and Klein in England believed that they had found the cause 
of milk-borne outbreaks of scarlet fever in the sickness of the 
cows supplying the milk. These findings have not been sub- 
stantiated, and the micrococcus which Klein believed was 
the cause of the disease has not been accepted as such by 



290 THE SOURCES AND MODES OF INFECTION 

bacteriologists. While many of the lower animals may be 
successfully inoculated with diphtheria, the disease does not 
appear often to occur spontaneously among them. Never- 
theless two milk-borne outbreaks have been traced to diph- 
theria of the cows' udder. One of these was reported by Dean 
and Todd 1 and the other by Ashby. 2 

Human Sources. — Besides the bacteriological evidence 
that milk rarely acquires its infection of these diseases from 
animals, we have the direct evidence that in a considerable 
number of outbreaks the milk is known to have been handled 
by persons sick with the disease or carrying its organisms. 
Trask 3 says that in 113 of the 179 outbreaks of typhoid fever 
reported by him an infected person was found to have 
handled the milk, and in only 4 instances was the infection 
reported to have come from polluted water used in washing 
utensils, and in 4 others to the use of milk bottles from infected 
houses. In 35 of the 57 scarlet-fever outbreaks an infected 
person was found to have handled the milk, and 3 others were 
due to the use of bottles from infected houses. Of the 23 
diphtheria outbreaks, 18 were traced to handlers of the 
milk. A study of the details of milk outbreaks shows that in a 
large proportion the infecting case was not recognized as such, 
that the symptoms were mild or atypical, that infection oc- 
curred during the incipient stage, or that the person was 
merely a carrier. Infection may occur at any time during the 
handling of milk, from the beginning of milking until the milk 
is delivered to the consumer, and it may also be caused by those 
who take care of the pails, cans, bottles, strainers, drums, etc. 
Outbreaks are believed to have been caused by the tasting of 
milk by infected dealers, and in the instance reported by 
Shoemaker 4 a convalescent patient was in the habit of start- 

1 Dean and Todd, J. Hyg., Cambridge, 1902, II, 194. 

2 Ashby, Pub. Health, Lond., 1906-07, XIX, 145. 

3 Trask, U. S. Pub. Health & Mar. Hosp. Serv., Hyg. Lab., Bull. 
No. 41, 25 et seq. 

4 Shoemaker, J. Am. M. Ass., Chicago, 1907, LXVIII, 1748. 



INFECTION BY FOOD AND DRINK 291 

ing a siphon from the milk drum by sucking the tube. It 
is also believed by many that flies are an important factor 
in the contamination of milk. 

^ Protection of Milk. — There are various ways in which the 
danger from infected milk may be avoided. 

First. If all recognized cases of the diseases just considered 
are promptly reported, and proper measures of isolation are 
insisted on, there will be a considerable decrease in the 
amount of milk-borne infection. When such a disease occurs 
in the family of a milk producer or dealer the patient should 
usually be removed from the premises, and the vessels, etc., 
if possibly infected, should be disinfected. The greatest diffi- 
culty is encountered in the management of convalescents, 
and particularly carriers, and it is the view of most health 
officers that the latter should be permanently excluded from 
the milk business. Unfortunately there are many mild cases 
of contagious disease which are never recognized and are not 
likely to be. Moreover, persons in the incipient stage are 
quite likely to transmit the disease, and we cannot hope for 
much earlier recognition than we now have. Hence for the 
prevention of outbreaks from these unknown sources we must 
rely on other methods. 

Second. It is possible to reduce the chances of infection 
by insisting on cleaner methods in handling milk and requir- 
ing the sterilization of all vessels, particularly of bottles. If 
all handlers would wash their hands, and keep their hands 
out of the milk and out of the vessels, there would be no milk 
outbreaks. But we can hope for no very radical improvement 
as regards the cleanliness of milkers, farm hands and peddlers. 

Third. The pasteurization of the milk by the dealer before 
delivery would also decrease to a large extent the amount of 
milk-borne disease, for a study of outbreaks shows that in a 
large proportion the infection of the milk takes place on the 
farm. But there is also considerable risk of contamination in 
the hands of the dealer after pasteurization. 

Fourth. Doubtless the most successful way of preventing 



292 THE SOURCES AND MODES OF INFECTION 

milk-borne disease at the present time is for the public to 
consume no milk except that which has been pasteurized or 
scalded in the house. Many object to the trouble and do not 
like the taste of heated milk, so that this practice is not likely 
to become universal. Moreover outbreaks have occurred, as 
at Bristol, 1 where milk pasteurized in an institution has been 
afterwards infected by a maid. 

It therefore seems that while it is possible materially to 
lessen by the above methods the amount of milk-borne 
disease, we cannot hope at present entirely to do away with 
the danger of milk-borne outbreaks of the diseases we have 
been considering. 

Ice Cream. — As milk is so frequently the bearer of disease, 
it ,is not surprising that outbreaks have at times been at- 
tributed to food products derived from milk. Thus Soper 2 
reported an outbreak due to the use of cream on breakfast 
food, and one of the outbreaks reported by Trask was due to 
whipped cream. Sedgwick and Winslow 3 collected records 
of four outbreaks of typhoid fever due to the use of ice cream, 
and another has been reported by Barras. 4 

Butter. — While it has been shown that typhoid bacilli 
may live for some time in butter, no outbreaks seem to have 
been reported as arising from the use of this substance. This 
is probably due partly to the fact that the germs must die 
off pretty rapidly, leaving perhaps only a few survivors, and 
partly to the difficulty of tracing an outbreak to such a 
source. 

Views concerning Tuberculosis. — Of all the animal 
diseases which are transmissible to man tuberculosis has 
received the most attention. After many years of discussion 

1 Davies and Walker, Proc. Roy. Soc. Med., Lond., 1908, Epi- 
demiol. Sec, 175. 

2 Soper, J. Mass. Ass. Bds. Health, Bost., 1904, XIV, 68. 

3 Sedgwick and Winslow, Mem. Am. Acad. Arts & Sc, 1902, XII, 
No. 5, 475. 

4 Barras, Lancet, Lond., 1904, II, 1281. 



INFECTION BY FOOD AND DRINK 293 

and investigation there is now general agreement fhat while 
the two types of tubercle bacilli, human and bovine, are dis- 
tinct and quite permanent, the}' are reciprocally infective, 
though not to the same degree. That human beings may 
become infected with tuberculosis derived from cattle is now 
generally admitted, but there is as yet no general agreement 
as to the amount of such infection, though present views are 
not so divergent as those of a few years ago. The question 
of the mode of infection in tuberculosis and the source of the 
bacilli is so largely dependent on pathological evidence that 
it is very difficult for one who is not a pathologist properly to 
weigh the evidence. Yet in view of the lack of agreement 
among pathologists it becomes necessary for the health officer, 
who must take definite action to combat the disease, to 
attempt to arrive at some sort of conclusion. It seems fair, 
from the evidence thus far available, to draw the following 
conclusions: 

Bovine Bacillus may infect Man. — First. The bovine 
type of bacillus is capable of causing infection in human 
beings. This is shown by the successful inoculation of human 
beings with bovine virus. A considerable number of cases 
of the accidental inoculation of veterinarians and laboratory 
workers while manipulating animals dead with tuberculosis 
have been reported by Pfeiffer, Tscherning, Naughton, Cop- 
pez, Priester, Hartzell, Grothan, Jadasohn, Ravenel, de 
Jong, 1 Salmon 2 and others. In most cases the lesion was 
local, and some have argued that this is strong evidence of 
weakened virulence for man. The finding of the bovine type 
of the bacillus in human beings is generally considered as 
furnishing a more certain demonstration of the latter 's suscep- 
tibility to the disease. As will be again referred to, the ( ler- 
man and British commissions, and various Americans, have 

1 Moss, Johns Hopkins Hosp. Bull., 1909, XX,39;Cornet, NothnageTa 
Encyclopedia of Practical Medicine, Phila, <fc Loud., L907, Tubereu- 

losis, 77. 

» U. S. Dept. Agric, Bu. An. Ind., Bull. No. 33, !•■• 



294 THE SOURCES AND MODES OF INFECTION 

found the bovine bacillus in from 16 to 25 per cent of the 
cases studied. These facts, while demonstrating the suscep- 
tibility of human beings to the bovine form of the disease, 
do not indicate definitely to what extent the bovine type 
prevails in man, as the cases examined were usually specially 
selected. 

Feeding Experiments. — Second. Tuberculosis may be 
produced experimentally in animals by the ingestion of mate- 
rial containing tubercle bacilli. Milk known to be infected 
with tubercle bacilli has been in numerous instances fed to 
guinea pigs, rabbits, dogs, calves, swine and monkeys, and 
has caused fatal tuberculosis in them. This has been demon- 
strated by a large number of workers in all parts of the world. 
A good summary of previous experiments is given by Mohler, 1 
who himself produced tuberculosis by feeding guinea pigs 
with milk from tuberculous cows. Subsequent experiments 
by the Bureau of Animal Industry 2 show that while guinea 
pigs are with difficulty infected by feeding, hogs are very 
easily infected, the primary infection apparently occurring in 
the submaxillary glands, the lungs usually becoming second- 
arily infected. 3 That the ingestion of tuberculous material, 
especially milk from creameries, is the chief cause of tuber- 
culosis in swine, is the opinion of the officers of this depart- 
ment and of Ravenel and Russell. 4 The more recent work 
of Calmette and the French school, while not always including 
direct experiments with milk, show that material containing 
tubercle bacilli, introduced in any way into the stomach or 
intestines, results in the production of tuberculosis, and even 
the pupils of Flligge admit that the ingestion of a sufficient 
number of bacilli will cause the disease, though it is produced, 
they say, much more easily by inoculation or inhalation. It 

1 Mohler, U. S. Dept. Agric., Bu. An. Ind., Bull. No. 44, 13. 

2 U. S. Dept, Agric, Bu. An. Ind., Circ. 83, Bull. Nos. 86, 88, 93. 

3 Bull. No. 88, 40. 

4 Ravenel and Russell, Am. Pub. Health Ass. Rep., 1906, XXXII, 
Pt. I, 139. 



INFECTION BY FOOD AND DRINK 295 

is also generally admitted that bacilli may be absorbed 
through the intestines without leaving any lesion. While 
some pathologists think that it is usually possible to deter- 
mine the route of infection by the age and character of the 
lesions, other equally good men do not consider that any very 
reliable conclusions can be arrived at in this manner. Under 
these circumstances it appears that we cannot as yet appeal 
to the pathologists for a definite decision as to the mode of 
infection in this disease, and we may be permitted to assume 
that a large amount of tuberculosis may be due to infection 
through one part or another of the alimentary canal. 1 

Tubercle Bacilli in Milk. — Third. Tubercle bacilli are 
frequently found in cows' milk. It was formerly believed 
that tubercle bacilli do not occur in cows' milk unless the 
udder is diseased. Nevertheless various observers from time 
to time have reported finding the bacilli although no udder 
disease was evident. Finally Schroeder and Cotton 2 showed 
that frequently the feces of cattle contain large numbers of 
tubercle bacilli, although the animals present no visible symp- 
toms of disease. They furthermore showed that the pollu- 
tion of milk with infected feces is the most common source 
of tubercle bacilli found in milk. As from 3 to 50 per cent 
of the cattle in different parts of the United States react to 
tuberculin, and probably 25 per cent of the cattle in Great 
Britain are infected, it is not surprising that market milk in 
these countries is frequently found to contain tubercle bacilli 
in sufficient numbers to cause the death of test animals. 
Anderson 3 gives a resume of the literature of the subject. 
Among the percentages of infected milk referred to are, in 
Copenhagen, 14.3 per cent ; Boston, 21 per cent and 40 per cent ; 
Liverpool, 5.2 per cent from city dairies, 13.4 per cent from 

1 For other references to the causation of tuberculosis through the 
alimentary canal see p. 255. 

2 Schroeder and Cotton, U. S. Dept. Agric, Bu. An. Ind., Bull. No. 90. 

3 Anderson, U. S. Pub. Health and Mar. Hosp. Serv., Hyg. Lab., 
Bull. No. 41, 163. 



296 THE SOURCES AND MODES OF INFECTION 

country dairies, though later, 1 owing to the efforts of the 
authorities in eradicating the disease, the percentage in city 
dairies was 1.4 per cent and in country dairies was 7 per cent; 
Genoa, 9 per cent; London, 22 per cent; and Berlin, 28 per 
cent. Recently of 620 samples of milk consigned to London, 
61, or 11.6 per cent, were found to contain tubercle bacilli. 2 
Anderson found 6.72 per cent of 223 samples of market milk 
in Washington to contain virulent tubercle bacilli. Hess 3 
found virulent tubercle bacilli in 16 per cent of 107 samples 
of New York market milk (not bottled). He thinks the 
reason that his percentages are higher than those of Anderson 
is the employment of more test animals and the injection of 
the cream as well as the milk. He also found virulent 
tubercle bacilli in one of eight samples of commercially " pas- 
teurized" milk. In Manchester, England, 7.7 per cent of 542 
samples of milk were found to be infected. 4 

Danger Less than Supposed. — There seems to be no 
doubt that a large part of the milk consumed in Europe and 
the United States contains tubercle bacilli in numbers suffi- 
cient to cause the disease in test animals. It also seems to 
be certain that in the lower animals at least, particularly in 
young individuals, the ingestion of this tuberculous milk will 
cause not only tuberculosis of the alimentary canal, but will 
produce pulmonary disease and generalized tuberculosis also. 
It is probable that the ingestion of such milk by human be- 
ings will produce similar results. There is, however, consider- 
able variation in different kinds of animals as regards their 
susceptibility to this sort of infection. Even in animals as 
susceptible to the disease as are guinea pigs, infection by the 
ingestion of milk under normal conditions is not very easy. 
Thus Schroeder and Cotton 5 fed 132 guinea pigs with tuber- 

1 Rep. on Health of Liverpool, 1906, 189. 

2 Rep. Med. Off. Health, Lond., 1908, 60. 

3 Hess, Sixth Internat. Cong, on Tuberc., Wash., 1908, IV, 523. 

4 Rep. on Health of Manchester, 1906, 187. 

6 Schroeder and Cotton, U. S. Dept. Agric, Bu. An. Ind., Circ. 
No. 83. 



INFECTION BY FOOD AND DRINK 297 

culous milk on the average for forty-seven days, and only 1, 
which was fed for 357 days, contracted the disease. This 
was only 0.76 per cent. At the same time 14.28 per cent of 
the guinea pigs exposed in the mangers of the cows from which 
the milk was obtained developed tuberculosis. Dr. Ver- 
ranus Moore writes me that he knows of a small village 
where most of the people received the milk from a herd 
of cattle that later was found to be extensively diseased; 
that is, about 77 per cent reacted to tuberculin and some 
2 or 3 per cent showed the disease on physical examination, 
and a considerable percentage of the guinea pigs inoculated 
with the mixed milk from the herd died of tuberculosis. 
This community had used this milk for a number of years. 
After the facts as stated above were ascertained the condi- 
tion was changed and up to this time there has not occurred 
a single case of recognized tuberculosis. Hess l examined 18 
children who a year previous had been known to be consum- 
ing tuberculous milk. None of them showed any visible signs 
of tuberculosis, though 4 reacted to the tuberculin test. Of 
100 children at Randalls Island, N. Y., fed on milk from 
tuberculous cows, none developed the disease. 2 A recent 
note, 3 which I have not had the opportunity to verify, gives 
the results of some observations made by Weber of the Ger- 
man Imperial Health Office on the use of tuberculous milk. 
From January, 1905, to April, 1908, 69 cows with tuberculosis 
of the udder were kept under observation, the milk from 
which was consumed raw by 360 persons, of whom 159 
were children. Of these, 5, of whom 2 were between 1 
and 2 years of age, were " indubitably infected with tuber- 
culosis through the use of the milk." The children had 
taken the milk of these cows from one to one and a half 
years. In both cases the milk was used raw by all the mem- 
bers of the family, the parents and several children; all these 

1 Hess, J. Am. M. Ass., Chicago, 1909, LI I, 10 11. 

2 Park, Sixth Internat. Cong, on Tubcrc, Wash., L908, I, 150. 
» J. Am. M. Asa., Chicago, 1910, LIX, 880. 



298 THE SOURCES AND MODES OF INFECTION 

people remained healthy. In the sick children there was 
merely an affection of the cervical glands in which tubercle 
bacilli of the typus bovinus were demonstrated by bacteri- 
ological tests. There were no other symptoms. Whitla, 1 
however, reports an instance where of 150 children fed on 
milk known to be tuberculous, 15 contracted the disease. 

Percentage Due to Bovine Infection. — It has thus far 
been shown merely that human beings may contract tuber- 
culosis by drinking the milk of tuberculous animals. It re- 
mains to determine, if possible, how great this danger really 
is. Various attempts have been made to estimate this. It 
has been assumed by some that intestinal tuberculosis, and 
to some extent generalized tuberculosis without preponderant 
pulmonary involvement, is indicative of infection by ingesta, 
and presumably by milk. The fact that these types of the 
disease are more common in children, of whose diet milk 
forms a relatively large part, has been thought to lend color 
to this view. It is not improbable, however, that the dif- 
ferent form which the disease presents in early life may be 
due to the characteristics of the age rather than to the mode 
of infection. Children certainly consume a relatively large 
amount of milk, btft tuberculosis is not so common among 
them as among adults. In Providence only about 15 per cent 
of the tuberculosis is in children under five years of age, and 
only about 4 per cent of the tuberculosis death rate is attrib- 
uted to abdominal tuberculosis. In the registration area of 
the United States abdominal tuberculosis accounts for about 
3.5 per cent of all deaths from this disease. This form of 
tuberculosis appears to be much more common in England. 2 
But careful observers find that contact with other cases is 
probably responsible for a large proportion of tuberculosis in 
children. Park 3 states that of 100 cases of glandular and 
bone tuberculosis in St. Mary's Hospital, New York, 44 per 

1 Whitla, Lancet, Lond., 1903, II, 135. 

2 Bovaird, Sixtli Internat. Cong, on Tuberc, Wash., 1908, II, 446. 

3 Park, Sixth Internat. Cong, on Tuberc., Wash., 190S, I, 157. 



INFECTION BY FOOD AND DRINK 299 

cent had been in close contact with tuberculous cases. 
LaFetra 1 found 40.4 per cent of 131 cases of tuberculosis in 
infants, probably due to family infection. Comby a considers 
family infection of prime importance in the tuberculosis of 
children. Floyd and Bowditch 3 found that 679 of 1000 
tuberculous children had been in contact with the disease in 
their homes. Approaching the subject in another way, they 
found signs of the disease in 66 per cent of 746 children living 
in tuberculous families among the poor. Miller and Wood- 
ruff 4 found the same true in 51 per cent of 150 children, and 
Sacks 5 in 53 per cent of 322 children. 

While there seems to be no doubt that tubercle bacilli may 
remain latent in the body for some time, there are very few 
who accept von Behring's view that most human tubercu- 
losis is acquired in childhood from drinking tuberculous cows' 
milk. As greatly discrediting von Behring's theory may be 
mentioned the investigations of Speck, 6 who found that of 
8010 cases of tuberculosis only 27 per cent had been fed on 
cows' milk in infancy. Von Ruck 7 found that certainly not 
over 25 per cent, and possibly not over 10 per cent, had been 
brought up on cows' milk. Flick 8 obtained similar evidence 
at the Phipps Institute in Philadelphia. Heymann 9 says 
that in Christiania, where nearly all the infants are nursed, 
tuberculosis is more common than in Bavaria, where artificial 
feeding is very common, and that in Prague, where nearly all 

1 LaFetra, Sixth Internat. Cong, on Tuberc, Wash., 1908, II, 361. 

2 Comby, Sixth Internat. Cong, on Tuberc, Wash., 1908, II, 503. 

3 Floyd and Bowditch, Boston M. & S. J., 1908, CLIX, 783. 

4 Miller and Woodruff, Sixth Internat. Cong, on Tuberc., Wash., 
1908, II, 487. 

5 Sacks, Sixth Internat. Cong, on Tuberc, Wash., 190X, II, 479. 

6 Speck, Ztschr.f.Hyg.u.Infectionskrankh., Leipz.,1904, XL VIII, 27. 

7 Von Ruck, J. Am. M. Ass., Chicago, 1905, XLIV, 1360. 

s Flick, Report of Henry Phipps Inst. Study . . . Tuberculosis, 
Phila., 1906, IV, 49. 

9 Heymann, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1901, 
XLVIII, 45. 



300 THE SOURCES AND MODES OF INFECTION 

babies are breast fed, the tuberculosis death rate is as high 
as in any city in Europe. I am inclined to the opinion that 
such epidemiological facts as we have indicate that children 
are more susceptible to the human than to the bovine type 
of the disease, and there seems to be as much clinical evidence 
that the tuberculosis of childhood is due to family infection 
as is the tuberculosis of adult life. 

Instances of Milk Infection. — Instances are not rarely 
reported in which there is considerable evidence of the pro- 
duction of tuberculosis in children by the use of milk from 
tuberculous animals. One of the most convincing is that 
narrated by Adams of Aberdeen and summarized by Hess. 1 
Two children of a farm laborer died of tuberculous meningitis 
in January and March of 1907. There was no known expo- 
sure to the disease except the use of milk from a cow with 
tuberculosis of the udder. Bacilli identical in type with those 
found in the cow were recovered from the cerebro-spinal fluid 
of one of the children. Most of the cases reported are not 
so convincing as this, and in many the evidence is decidedly 
weak and would not stand critical examination. The evidence 
afforded by these cases is not of much value, for though some 
of the cases are doubtless caused'in the manner alleged, they 
merely indicate what is also suggested by animal experiments, 
— the possibility of human infection from milk. An estima- 
tion of the extent of this danger must be made in other ways. 

Proportion of Human and Bovine Types. — Since the sig- 
nificance of Theobald Smith's discovery of the difference 
between the bovine and human types of the tubercle bacillus 
has been recognized, the relative frequency of the two types 
in human beings has been used as a measure of the impor- 
tance of milk infection, for it is conceded that it is through 
milk almost exclusively that bovine tuberculosis is trans- 
mitted to human beings. Much care and labor are involved 
in the differentiation of the two types, but the number of 
observations made is considerable, among which those of the 
1 Hess, J. Am. M. Ass., Chicago, 1909, LII, 1015. 



INFECTION BY FOOD AND DRINK 301 

German and British commissions are notable. Moss 1 sum- 
marizes the cases previously reported. In all there had been 
306 cases investigated, in 63, or about 20 per cent, of which 
bovine bacilli were found. But it must not be inferred from 
this that 20 per cent of all cases of human tuberculosis would 
present this type. With the exception of 54 cases in adults 
studied by the German commission, most of the cases have 
been children with the intestinal or glandular forms of the 
disease. In the 54 adults no bovine bacilli were found. The 
bovine type of bacillus has rarely been found in pulmonary 
tuberculosis, even among children. It may perhaps be in- 
ferred that 25 per cent of bone and glandular tuberculosis in 
children is due to the bovine bacillus. But Tendeloo 2 calls 
attention to the fact that if the bovine type of bacillus is a 
permanent one, — and unless it is these observations are of 
little value, — the above figures are probably misleading, for 
the bovine bacillus if permanent will be transmitted from 
man to man and does not always indicate a bovine origin. 
As only about 15 per cent of the tuberculosis in the United 
States is of the form in which the bovine bacillus is found, 
and as only about 25 per cent of the cases show this type of 
bacillus, we are justified, using the type as a test, in assuming 
that only about 5 per cent of our tuberculosis is derived from 
bovine sources. But this, while a small percentage, would 
amount to almost 2500 deaths annually in the registration 
area of the United States, — certainly a number which ought 
to be considered. 

Epidemiological Evidence. — It seems to be a fact that 
tuberculosis, even those forms of the disease which are gen- 
erally supposed to be caused by milk, is not appreciably less 
in those parts of the world where cows' milk is little used, or 
where it is usually sterilized, or where there is little tubercu- 
losis among cattle. Kitasato 3 says that there is very little 

1 Moss, Johns Hopkins Hosp. Bull., 1909, XX, 39. 

2 Tendeloo, Sixth Internal Cong, on Tuberc., Wash., 1908, I, 87. 

1 Kitasato, Ztse.hr. f. Hyg. u. Infectionskrankh., Leipz., 1904, 
XLVIII, 471. 



302 THE SOURCES AND MODES OF INFECTION 

tuberculosis among the cattle in Japan, and so few cows that 
the daily milk supply does not average 3 c.c. per capita, yet 
nearly 8 per cent of all deaths are due to tuberculosis, and in 
a series of autopsies 17 per cent of the tuberculosis cases were 
under eighteen years of age, and 10 per cent of the cases 
showed primary intestinal infection. Cobb says that substan- 
tially the same conditions prevail in China. According to 
Heymann x tuberculosis is very common in Greenland, where 
no cows' milk is used. Fisch 2 states that on the Gold Coast 
no milk is used, yet 12 per cent of the sick have tuberculosis. 
Tuberculosis prevails as extensively in Cuba as in the United 
States, but Dr. Guiteras tells me that milk is practically 
never used without scalding, and tuberculosis is comparatively 
rare among cattle. If, as appears from a study of the relative 
prevalence of the two types of bacilli, less than 5 per cent of 
all tuberculosis is due to cows' milk, the entire elimination of 
this factor would not, as, from the data furnished by Japan, 
Cuba, and other places, it appears that it does not, have any 
appreciable effect on the death rate from this disease. The 
total elimination of bovine tuberculosis, so far from " stamp- 
ing out the great white plague," as some assert, would prob- 
ably not make any noticeable difference in the tuberculosis 
death rate. Nevertheless it appears from present evidence 
that in the aggregate a large number of deaths are due to 
this cause, and if there is any practical method of reducing 
this cause of death, effort should be made to apply it. 

Protection against Tuberculous Milk. — Various ways are 
suggested for eliminating this danger from milk. Among 
these is the heating of milk to a sufficient temperature to kill 
tubercle bacilli as well as typhoid bacilli and other pathogenic 
organisms. Some have urged compulsory pasteurization by 
dealers, and this practice is, without any legislation, making 
rapid progress in cities. But, as is shown by Hess in New 

1 Heymann, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1904, 
XLVIII, 45. 

2 Fisch, Cor.-Bl. f. schweiz. Aerzte, 1904, XXXIV, 761. 



INFECTION BY FOOD AND DRINK 303 

York, commercial pasteurization does not always destroy 
tubercle bacilli, and the proposition that commercial pas- 
teurization be under the control of health officials is a timely 
one. As has already been stated, there are objections to the 
compulsory pasteurization of all milk sold, hence the federal 
Department of Agriculture 1 has suggested a classification of 
market milk into — 

First. Certified milk, which presumably would be free 
from danger and of high quality, and would be sold at a 
higher price to those who desired it. 

Second. Inspected milk, which also should be from cows 
free from tuberculosis, but which would not show so low a 
bacterial count as the certified milk and which could be sold 
for not much if any more than the next class. 

Third. All milk not produced under such rigid inspection 
should be pasteurized under municipal supervision. 

There certainly is a tendency, without any compulsion, for 
municipal milk supplies to become classified in the way above 
indicated. Another way of removing the danger is for the 
consumer to heat the milk after it is received from the dealer. 
In this way each consumer can protect himself from the dan- 
ger of contracting tuberculosis, typhoid fever and similar 
diseases. But most persons will not do this unless they are 
induced to do so by a slow process of education, and this 
education can scarcely be hastened without causing an 
unreasonable fear of milk, which will result in lessening the 
consumption of a cheap, digestible and nutritious article of 
food. It seems to me that what is needed is a better and 
more exact knowledge of the relations of milk to disease on 
the part of health officers and physicians, from which ought 
to follow a gradual education of the public, but without an 
alarmist propaganda, and then there will probably gradually 
develop a specialization in the milk business to meet the 
necessarily different needs of different people. 

1 U. S. Pub. Health & Mar. Hosp. Serv., Hyg. Lab., Bull. No. 41, 
559. 



304 THE SOURCES AND MODES OF INFECTION 

Eradication of Bovine Tuberculosis. — Another way of 
dealing with the tuberculous milk problem is to strive to eradi- 
cate bovine tuberculosis, or at least to eliminate from herds 
of milch cows all animals in the active stage of the disease. 
This is urged by many, and has been and is being attempted. 
It. is claimed by the federal and state departments of agricul- 
ture that the existence of bovine tuberculosis entails great loss 
upon the farmers, and if this is true, these departments should 
devise and urge means for eliminating the disease, but the 
expense should be borne by the farmers and not by the public. 
If, however, the restriction or elimination of bovine tubercu- 
losis is urged as a public health measure, as it so often is, we 
should count well the cost before placing it upon the general 
taxpayer. We ought to have a finer sense of financial per- 
spective in sanitary matters. The cost of efficient measures, 
if efficient measures have yet been devised, for eliminating 
bovine tuberculosis will be enormous, and we may well con- 
sider whether as good results from a public-health standpoint 
may not be secured, say by pasteurizing milk, and whether 
the money might not be expended in other ways with far 
greater results. It is very doubtful whether the expenditure 
of $100,000 a year for several years in a state like Massachu- 
setts would really result in stamping out the disease in cattle ; 
but consider how much such a sum would accomplish if spent 
in the establishment of dispensaries and the employment of 
district nurses, with perhaps $5000 to $10,000 used for fur- 
ther scientific study of the many unsolved problems connected 
with the causation, prevention and cure of the disease. 

Tubercle Bacilli in Butter. — From what is known of the 
viability of the tubercle bacillus, there can be no doubt that 
it will live for some time in butter. Schroeder and Cotton 1 
carefully investigated the subject and found virulent tubercle 
bacilli in butter after three months, and Trask 2 refers to a large 

1 Schroeder and Cotton, U. S. Dept. Agric., Bu. An. Ind., Circ. 
No. 127, 1898. 

2 Trask, J. Am. M. Ass., Chicago, 1908, LI, 1491. 



INFECTION BY FOOD AND DRINK 305 

number of similar observations. Cases of tuberculosis do not 
seem to have been traced to the consumption of such butter, 
and it is very unlikely that they would be traced even if they 
occurred. Owing to the small amounts of butter consumed, 
it is probable that very few cases of tuberculosis are caused 
in this way. Butterine also has been shown to be infected 
from the milk, fat and butter of which it is made. 1 Owing 
to the mode of making and the time occupied in curing 
cheese, virulent tubercle bacilli are probably rarely if ever 
found in it. 2 

Mediterranean Fever from Milk. — Mediterranean fever, 
which is an important disease around the shores of the 
Mediterranean, has been considered on a previous page, and 
reference made to the brilliant researches of Bruce, Horrocks 
and others, who determined that it is primarily a disease of 
goats, and only incidentally transmitted to man through the 
medium of milk. The obvious remedy is to avoid the use of 
goats' milk whenever these animals are known to be infected, 
and in the Malta garrison the disease has by this means been 
eliminated. It is rather surprising that in view of the known 
facts the United States Department of Agriculture should in 
1905 have imported a large number of goats from Malta, 
but the importation resulted in a complete demonstration of 
the infectiousness of the milk, for quite a number of persons on 
the ship, and one in America, developed the fever as a result 
of drinking the milk. The goats have now all been killed. 

Anthrax from Milk. — Experiments have shown that 
anthrax bacilli may be absorbed through the intestines, 
and they are found in the milk of diseased animals. 3 In- 
stances of this mode of infection in man have been reported, 
but they are certainly very rare. 4 

1 U. S. Dept. Agric, Rep. Bu. An. Ind., 1907, XXIV, 152. 

2 Harrison, U. S. Dept. Agric., Rep. Bu. An. Ind., 1902, XIX, 217. 

3 Horrocks, J. Roy. Army Med. Corps, Lond., 1908, XI, 46. 

4 Teacher, J. Comp. Path. & Therap., Edinb. & Lond., 1906, XIX, 
225; Meyer, Deutsche med. Wchnschr., 1908, XXXIV, 108; J. Hyg., 
Cambridge, 1909, IX, 279, 315. 



306 THE SOURCES AND MODES OF INFECTION 

Foot-and-Mouth Disease. — Foot-and-mouth disease is 
said to be transmitted to human beings by means of milk, 
and according to Salmon such cases are frequently reported 
in European outbreaks, 1 but none occurred during the last 
outbreak in Massachusetts, perhaps owing to the fact that 
suitable precautions were taken. An instance of this sort of 
infection occurred near Boston in 187 1. 2 Kober 3 refers to 
other instances of the transmission of foot-and-mouth disease 
by milk. 

Rabies from Milk. — According to Kober, 4 Nocard proved 
experimentally that rabies could be conveyed in milk, and 
Burdach infected animals with the milk of a woman sick with 
the disease at the Pasteur Institute. Repetto 5 was able to 
kill rats by feeding them with rabies virus, and Remlinger 6 
did the same. Dr. Austin Peters of Boston writes me that 
" Several times where cows have had rabies I have had milk 
taken from them and brought to the Harvard Medical School. 
Rabbits and guinea pigs inoculated with it have never devel- 
oped rabies. From this I should say that there is very little 
danger of rabies being carried through the milk." 

Other Animal Disease and Milk. — As regards actinomycosis, 
botryomycosis, tetanus, cowpox and many other animal 
diseases, little or nothing is known about their transmission 
by milk. 

Diarrhea from Milk. — The diarrhea of infants is prob- 
ably not a specific disease, but the group of disturbances 
which pass under this name are likely to be due to infection by 
a number of organisms, and perhaps to some extent to intoxi- 
cation with the products of bacterial growth outside of the 

1 U. S. Dept. Agric, Rep. Bu. An. Ind., 1902, XIX, 405. 

2 Marion, J. Mass. Ass. Bds. Health, Bost., 1903, XIII, 11. 

3 Kober, Milk in Relation to Public Health, Senate Doc. No. 441, 
57th Congress, First Session, 1902, 154. 

4 Kober, Idem, 157. 

5 Repetto, Compt. rend. Soc. biol., Paris, 1908, LXIV, 716; Abst. 
Am. J. Pub. Hyg., Bost., 1909, XIX, 426. 

6 Remlinger, Compt. rend. Soc. de biol. Par., 1908, LXV, 385. 



INFECTION BY FOOD AND DRINK 307 

body. Among the bacteria suspected of causing diarrhea 
are B. coli, B. enteritidis sporogeiies, B. enteritidis (Gartner), 
B. dysenteric, B. paratyphosus and Streptococcus enteritidis. 

The summer diarrheas are confined principally to infantile 
life, the chief incidence falling on the last half of the first 
year. According to Newsholme 1 they are associated with a 
deficient rainfall, and their dependence upon a high tempera- 
ture is particularly marked. A very large proportion of the 
deaths occur during the hot summer months, and the hotter 
the season, as a general thing, the higher the mortality. The 
relation between temperature and this disease is probably 
more or less indirect, and at present is not well understood. 
Another marked characteristic of the summer diarrheas is 
that they are intimately associated with the mode of feeding. 
Breast-fed infants are very little affected, while artificially 
fed infants suffer severely. As the artificial food of infants 
is chiefly cows' milk, and as these diseases appear to be of 
bacterial origin, and as the growth of bacteria in milk is 
enormously facilitated by hot summer weather, it is generally 
assumed that diarrhea is due to the growth of infective organ- 
isms in the milk. Some, however, doubt the validity of 
this assumption. Liefmann 2 considers that artificial feeding 
causes disturbances of digestion and nutrition, and that these 
lay the foundation and open the way for new and injuri- 
ous factors. The latter are mostly bacterial, and the bacteria 
effect an entrance into the child's body in various ways, 
usually by contact infection, and not so often by milk as has 
been commonly supposed. He says that the use of sterilized 
milk is disappointing, which indicates that milk is not the 
chief vehicle of the infection. 

Epidemiological Studies. — In 1901-02 a very valuable 
series of observations was undertaken in New York by 
Park and Holt, under the auspices of the Rockefeller Insti- 

1 Newsholme, Pub. Health, Lond., 1899-1900, XII, 139. 
* Liefmann, Ztsrhr. f. Hyg. u. Infectionskrankh., Leipz., 1908-09, 
LXII, 199; Abst. Pub. Health, 1909, XXII, 430. 



308 THE SOURCES AND MODES OF INFECTION 

tute. 1 It appeared to these observers that lack of care in the 
feeding and general management of the babies had more to do 
with the development of diarrhea than had the character of 
the milk. It is true that exceptionally dirty store milk gave 
worse results than any other, but the users of this milk were 
poorer and dirtier and gave less intelligent care to their 
children. A rather limited number of children were fed on 
fairly good milk raw, and another group on the same milk 
pasteurized, other conditions being nearly the same. Those 
on pasteurized milk had much less diarrhea, but the authors 
state that a considerable percentage do quite as well on raw 
milk. Condensed milk was found to be associated with a 
large percentage of diarrheal cases. Intelligent care and feed- 
ing seem to the authors more important than the character 
of the milk. They also consider the infection of the milk in 
the home or store as a very important factor. Breast-fed 
babies are not immune to diarrhea, and Newsholme, 2 in a 
very careful study of the subject at Brighton, found that 6.6 
per cent of the deaths from diarrhea were in breast-fed infants, 
who almost certainly could not have been infected by the 
milk. Newsholme pertinently asks why, if these cases were 
not due to milk, should it be assumed that all the artificially 
fed infants who succumbed to diarrhea met their death because 
of milk contamination. From a study of the kinds of milk used 
in Brighton it was found that more diarrhea was associated 
with the use of condensed milk than with that of any 
other. Similar results from the use of condensed milk were 
found by Richards in the neighboring city of Croydon, 3 and 
by Sandilands in Finsbury, London, 4 and their findings do 
not differ materially from those of Park and Holt. In the 
English cities a very good brand of condensed milk, viz. 
Nestles', was the one chiefly employed, and Sandilands found 

1 Med. News, N. Y., 1903, LXXXIII, 1066. 

2 Newsholme, J. Hyg., Cambridge, 1906, VI, 139. 

3 Rep. Med. Off. Health, Croydon, 1904, 1908. 

4 Sandilands, J. Hyg., Cambridge, 1906, VI, 77. 



INFECTION BY FOOD AND DRINK 309 

it very free from bacteria. He also states that this condensed 
milk is collected and put up in Switzerland in such a manner 
as to make infection during the process much less likely than 
in ordinary market milk. All the writers above referred to 
consider that these facts indicate that the infective material 
of infantile diarrhea gets into the milk and other food to a 
large extent in the home. Newsholme especially insists on 
this, and he attributes not a little to direct contact. Tomp- 
kins, 1 from a study of the very local distribution of the disease 
in Leicester, concluded that it must have its source in local 
conditions. Robertson and Niven, from a study of cases in 
their respective cities of Birmingham and Manchester, believe 
that the infection takes place in the city chiefly, either by 
direct infection or through the milk. 

Explosive Outbreaks of Diarrhea. — Sometimes what 
appear to be explosive milk-borne outbreaks of diarrhea 
occur. Several such are referred to by Newman. 2 Recently 
a very interesting outbreak of this kind has been reported 
by Hay. 3 Various bacteria, such as B. coli, B. enteritidis 
sporogenes and B. enteritidis of Gartner, have been isolated 
from the milk in such cases and also from the evacuations 
of the patients. It is uncertain whether such outbreaks have 
any connection with ordinary summer diarrhea, though that 
they have is the view of Delepine, 4 and he believes that the 
contamination of milk usually takes place at the farm. 

Prevention of Diarrhea. — It appears, then, that we have 
very little accurate knowledge as to the causation of infantile 
diarrhea. It certainly has some intimate relation to the diet, 
but exactly what is not known. We do know, however, that 
the most efficient means we have of combating it is correct 
feeding. Breast feeding is far superior to anything else, but 
good success can be obtained with the careful and scientific 

1 Tompkins, Brit. M. J., Lond., 1889, II, 180. 

2 Newman, Infant Mortality, Lond., 1906, 170. 

3 Hay, Pub. Health, Lond., 1910, XXIII, 180. 
* Delepine, J. Hyg., Cambridge, 1903, III, 89. 



310 THE SOURCES AND MODES OF INFECTION 

use of good cows' milk. Pasteurized milk appears to be better 
than dirty raw milk of high bacterial count, but there does 
not seem to be any definite connection between the disease 
and an increasing bacterial content. The longer milk re- 
mains exposed in shops and houses, the more dangerous it 
seems to be. Almost all who have had to do with modern 
milk stations, either those using pasteurized milk or those 
dispensing clean raw milk, agree that the larger part of the 
resulting good is due to the education of the mother in 
the care of her child. The chief thing, then, is to teach the 
mothers how to modify, keep and feed milk. ' It is of impor- 
tance, too, that the mothers should be enabled to get fairly 
clean and fresh milk. In some cities it is doubtless necessary 
to establish milk stations for this purpose, which dispense 
either pasteurized milk, or preferably clean raw milk. In 
Providence stations were found to be unnecessary, as there is 
no part of the city in which it is not possible to get 18 to 24 
hours' old milk with less than 50,000 bacteria per c.c, and a 
number of dealers furnish milk below 10,000. This milk is 
sold by the producer in glass bottles and at the ordinary 
market price. The milk is by no means equal to certified 
milk, but the observations of Park and Holt, and our expe- 
rience in Providence, seem to show that milk of the grade 
above indicated is ordinarily as little likely to cause infantile 
diarrhea as is certified milk. Only a small amount of the milk 
supply of a city is used for feeding infants, and it seems un- 
necessary to insist on a high grade of expensive milk for all 
consumers. At present it is more economical to bring the 
existing good supplies to the knowledge of the mothers 
through physicians, the health department, district nurses 
and milk stations. In cities up to 200,000 or 300,000 it is 
probable that enough dealers can be found to supply the 
necessary demand for a good though not certified milk. 



INFECTION BY FOOD AND DRINK 311 

Infection by Meat. 

Inspection of meat is considered by the public a matter of 
the greatest importance, but concerning many forms of meat 
infection we have little definite knowledge, and the danger of 
others has been greatly exaggerated, not only by the public, 
but also by physicians and health officials. Various animal 
parasites, such as tapeworms and trichinae, are derived from 
the lower animals through the use of their flesh as food, but 
a consideration of these is beyond our present purpose. One 
of these animal parasites, the trichina, is quite common in 
pork, and a considerable number of deaths are caused by it 
each year. 

Food Poisonings. — What are commonly called food poi- 
sonings, when resulting from eating meat, are due to two 
general causes. One class is the result of the action of various 
kinds of putrefactive organisms which infect the food after 
slaughter. These cases we need not consider. Another class 
results from infection of the flesh during the life of the animal, 
and is due, so far as known, to various members of the colon 
group, such as B. paratyphosus, B. enteritidis (Gartner) and 
B. morbificans. In many instances this unwholesome meat is 
derived from diseased animals, usually showing some sort of 
enteritis or septic infection. That the infection is always 
derived from diseased animals seems unlikely, for several 
observers have found in healthy animals the bacteria which 
are believed to be the cause. 1 Savage, 2 however, was un- 
able to isolate B. enteritidis (Gartner) from the intestines of 
23 healthy animals which he carefully studied. But from 
what is known of the relations of this group of bacteria to 
human beings we should expect to find them occasionally in 
healthy animals, convalescents and carriers. Unfortunately 
the toxins produced by these bacteria are not always de- 

1 Bolduan, Food Poisoning, New York, 1900, 33. 

2 Savage, Rep. Med. Off. of Local Gov. Bd., 1906-07, XXXVI, 253; 
1907-08, XXXVII, 425. 



312 THE SOURCES AND MODES OF INFECTION 

stroyed by heat, so that while cooking may kill the bacteria, 
cooked meat, which has been the seat of bacterial growth, 
has been known to cause sharp outbreaks characterized by 
acute gastrointestinal symptoms. If living bacteria of this 
group are present, infection with them may result, causing a 
slow after development of symptoms somewhat akin to those 
of typhoid fever. The cooking of meat cannot be relied upon 
wholly to prevent sickness arising from this sort of food 
infection. Government inspection is suggested as the only 
method by which these diseases can be prevented. If, how- 
ever, bacilli are found in healthy animals, it is questionable 
whether any amount of inspection would entirely eliminate 
the danger. How great the danger is it is difficult to deter- 
mined A good many outbreaks have been reported in Ger- 
many, aggregating thousands of cases, and reports come not 
rarely from England. No data are available for the United 
States. For several years I have been on the lookout for 
the reports of such cases in the medical press and in the 
" Index Medicus," and one year I employed a press-clipping 
bureau to secure cuttings from the lay press, but I have 
notes of scarcely more than a dozen outbreaks. Doubtless 
others occurred, but they cannot have been very numerous. 
A good many reports of instances of " ptomaine poisoning " 
find their way into the newspapers, which prove on investi- 
gation to have no basis in fact. 

Meat and Tuberculosis. — In the public mind the fear of 
contracting tuberculosis by eating meat is very considerable, 
and public sentiment is sufficient to support very stringent 
regulation of the sale of meat from diseased animals. Yet 
it does not appear that there is a single recorded instance of 
the transmission of disease in this way. And we should 
expect that if such were possible it would be exceedingly rare. 
Tubercle bacilli have their habitat in lungs, liver, intestines, 
glands and other viscera, and not usually in the muscle or 
fat. The tubercle bacillus is easily killed by heat, and very 
little of this class of food is eaten without cooking. Smoked 



INFECTION BY FOOD AND DRINK 313 

beef and ham are occasionally eaten without cooking, but even 
then considerable time is consumed in the process of corning 
and smoking, and in the rare cases in which a few bacilli 
are contained in the meat they are likely to have lost most 
of their virulence. As for the viscera, if they are used at all 
for food they are generally pretty well cooked, y Cornet states 
that Schottelius studied the use of meat from tuberculous 
animals in Wurzburg, and could not find a case of the disease, 
although the meat was eaten in every form. It has been 
said that while tuberculosis has been decreasing the consump- 
tion of meat has been increasing; and this is certainly an 
indication that the use of meat cannot be a factor of any 
great moment in the causation of the disease. At the most 
it is scarcely possible for the disease to be derived from this 
source except in rare instances. 

Conclusions. — The diseases which it is alleged may be 
transmitted by flesh foods are those caused by animal para- 
sites, of which trichinosis is the most important, diseased 
conditions produced by the colon group of bacilli, and tuber- 
culosis. The latter is a negligible quantity, the second group 
probably causes very few deaths in this country, while trichi- 
nosis is doubtless the most important disease transmitted in 
this manner. 

Federal Control. — The federal government has instituted 
an expensive meat -inspection service, ostensibly to guard the 
health of the public, but as trichinosis, the most common and 
serious of the animal diseases, though it is very rare in 
man, is ignored, it is suspected that the system was insti- 
tuted by Congress as the result of an ill-informed though 
popular demand. Filthy conditions in the slaughterhouses, 
and the killing of diseased animals, though their flesh may 
not be injurious to health, are shocking to the aesthetic sense 
and the public demands reform. Including the expense of 
inspection and the value of the meats condemned, the cost 
to the country is $5,000,000 or $6,000,000 per annum. It is 
true that the conditions of labor in the great packinghouses 



314 THE SOURCES AND MODES OF INFECTION 

have been improved, and that cleanlier methods of handling 
meat have been enforced, but it is doubtful whether any sick- 
ness among consumers has been prevented. I cannot help 
thinking how much ultimate good might have accrued if a 
tenth of the sum spent in meat inspection had been devoted 
to the systematic study of the many unsolved problems of 
sanitation, such as, for instance, the danger from fomites, the 
part played by air in the spread of disease, the causes of 
the decline of tuberculosis and the mode of extension of the 
disease, the relation of food to health, the causes of infantile 
diarrhea, the relation of water supplies to the general health, 
or the meaning of bad air and its effect on health. 

Infection by Shellfish. 

Oysters. — Since oysters and other shellfish are often 
eaten raw, and often live in sewage-polluted waters, they 
might be suspected, and indeed were suspected by Sir Charles 
Cameron as long ago as 1880, of being the cause of typhoid 
fever, and in 1893 Thorne suggested that the sporadic cases 
of cholera which appeared here and there in England were 
due to the eating of raw shellfish infected at the mouth of 
the Humber. The first demonstration of the relation of shell- 
fish to disease was by Conn. 1 He showed that 23 of 100 
students who went to a certain banquet developed typhoid 
fever, probably as a result of eating oysters. Of those who did 
not eat raw oysters none were sick, and one man who did not 
go to the banquet ate oysters at the dealers' and also was sick. 
The oysters had been kept about 300 feet from a drain leading 
from a house where there was typhoid fever. v ' Similar out- 
breaks have been reported by Chantemesse, 2 Mosny, 3 Chatin, 4 

1 Conn, Rep. St. Bd. Health, Connect., 1895, 253; Med. Rec, N. Y., 
1,894, XLVI, 743. 

2 Chantemesse, Bull. Acad, de med., Par., 1896, 3 s. XXXV, 588, 
724. 

3 Mosny, Rev. d'hyg., 1900. 

4 Chatin, Semaine med, 1897, XVII, 91. 



INFECTION BY FOOD AND DRINK 315 

Thresh and Wood, 1 a committee which studied the subject 
at Atlantic City, 2 Fraser, 3 Soper 4 and Morse. 5 

Clams, Mussels. — Clams as well as oysters have been 
believed to be the cause of outbreaks, 6 and where mussels 
and cockles are consumed raw in considerable quanti- 
ties they are equally liable to carry the infecting organ- 
isms. Three outbreaks in Norwich, England, in 1908 were 
traced to mussels. 7 Mussels also were believed to be the 
cause of an outbreak of typhoid fever in North Ormsby, 8 
and have been an important factor in the causation of 
typhoid fever in Belfast. 

Shellfish in English Cities. — Not only have shellfish been 
shown to be the cause of marked outbreaks of illness, as 
just shown, but they are strongly believed by many, espe- 
cially b} r English health officials, to be an important source of 
the ordinary " residual " t} T phoid fever occurring in cities. 
Newsholme 9 is especially insistent on this. A careful study 
of the matter in Brighton, where he was then health officer, 
showed that in 1894-96, of 189 reported cases of typhoid fever, 
41 were imported, and of the 148 remaining, 51, or nearly 30 
per cent, had eaten raw oysters or mussels within the incuba- 
tion period of the disease. These shellfish all came from 
grounds which were contaminated with sewage. From 1894 
to 1902, of 643 reported cases of typhoid fever, 158 were due 
to eating oysters and 80 to other shellfish, making in all about 
37 per cent due to this cause. Similar observations and con- 
clusions may be found in the reports of the health officers 
of Birmingham, Leicester, Southend, Manchester, London, 

1 Thresh and Wood, Lancet, Lond., 1902, II, 1567. 

2 Phila. M. J., 1902, X, 634. 

3 Fraser, Lancet, Lond., 1903, I, 183. 

4 Soper, Med. News, N. Y., 1905, LXXXVI, 241. 

5 Morse, Rep. St. Bd. Health, Mass., 1900, 836. 

6 Plowright, Brit. M. X, Lond., 1900, II, 681. 

7 Rep. on Sanitary Condition of Norwich, 1908, 14. 

8 The Medical Officer, 1909, II, 431. 

9 Newsholme, J. San. Inst., Lond., XVII. 



316 THE SOURCES AND MODES OF INFECTION 

Portsmouth and other places. The typhoid death rate in 
English cities is low and health officials find it difficult to 
account for the origin of the cases. The pollution of shellfish 
with sewage is not uncommon around the English and Irish 
coasts. 1 A considerable percentage of the cases of typhoid 
fever are known to have eaten shellfish, often from polluted 
sources, within two to four weeks of the date of attack. 
Perhaps the assumption is justifiable that some of these cases 
at least are due to the shellfish. Typhoid fever. has for some 
time been rather prevalent in Belfast, and a special commis- 
sion was appointed for its investigation. This commission 
believes that the chief source of the disease is mussels and 
cockles, picked up by the poorer people along the sewage- 
polluted flats. 2 Mair 3 states that in Belfast it was impossible 
to make a satisfactory canvass of the number of mussel users, 
either among the general population or among the typhoid 
patients. He bases his conclusions as to the part played by 
mussels on a careful statistical study, and shows that the 
disease in Belfast has varied according to changes in the 
amount of mussels consumed. He also shows that Jews and 
the wealthier classes, who use no mussels, had little typhoid 
fever. Nash 4 states that at Southend 54 per cent of the 
typhoid-fever cases confessed to the eating of shellfish, while 
only 0.4 per cent of 501 sick with other diseases confessed to 
such eating. Since the consumption of raw shellfish has 
decreased, typhoid fever has decreased also. In Leicester, 
50 per cent of the typhoid cases ate mussels, but they were 
used in only 15 per cent of a small number of non infected 
houses. Johnston 6 found that 25.8 per cent of 62 persons 

1 Rep. Med. Off. Loc. Gov. Bd., 1894-95, XXIV; Loc. Gov. Bd. for 
Ireland, Rep. on Shellfish Layings, 1904. 

2 U. S. Pub. Health & Mar. Hosp. Serv., Pub. Health Rep., Wash., 
1908, XXIII, 995. 

3 Proc. Roy. Soc. Med., Lond., 1909, II, Epidem. Sect., 187. 

4 Nash, Pub. Health, Lond., 1903-05, XVI, 80. 

5 Rep. Med. Off. Health, Leicester, 1908, 31. 

6 Johnston, The Medical Officer, II, 1909, 431. 



. INFECTION BY FOOD AND DRINK 317 

with typhoid fever had eaten shellfish, mussels and peri- 
winkles within a short time of their illness, while of 827 
other persons only 7.3 per cent had eaten them during the 
whole summer. In the United States, also, non-epidemic or 
" residual " typhoid has been attributed to the use of raw 
oysters, as in New York. 1 The chief reason for this seems 
to be that there is known to be a considerable consumption 
of sewage-infected oysters. 2 Most of the beds on which 
oysters are grown are free from dangerous pollution, but it 
is quite common to " fatten," i.e., freshen and swell them, in 
estuaries near sewer openings. 

Danger Variable. — It seems reasonable to conclude that 
the danger from eating sewage-infected shellfish is a real one. 
Exactly how great it is, is difficult to determine. In England 
anywhere from 15 to 50 per cent of the disease in cities is 
attributed to eating raw mussels or oysters, but this is on the 
supposition that every typhoid patient who has recently eaten 
raw shellfish derived the disease from that source. In Provi- 
dence raw oysters are very popular; they are consumed in 
restaurants in large numbers, and form a course in a large 
proportion of banquets and dinners. Many oysters are 
grown in the upper part of the bay, in water grossly contami- 
nated with sewage, and in the water and in the oysters 
colon bacilli are found. Until within two or three years, 
numbers of oysters from clean water have been " fattened" 
near sewer openings, yet Providence has a typhoid death 
rate tess than half that of the average American city. Oys- 
ters are not eaten to any extent in August, when typhoid 
fever begins to increase, and they are largely consumed in 
the winter and spring, when there is little of the disease. 
During the years 1902-05, of 263 typhoid-fever patients who 

1 Med. News, N. Y., 1904, LXXXIV, 325; 1905, LXXXV, 571. 

2 Report of U. S. Commissioner of Fisheries for year ending Jan. 30, 
19C4, Appendix, 189; Rep. Dept. Health, City of N. Y., 1904, I, 313; 
Rep. St. Bd. Health, New Jersey, 1904, 226; Rep. Dept. Health, Balti- 
more, 1907, 124. 



318 THE SOURCES AND MODES OF INFECTION 

replied definitely as to whether they had eaten oysters, only 
26, or about 10 per cent, said that they had. Very few raw 
oysters are eaten by laboring people, but at present laboring 
people furnish fully their share of typhoid fever. 

While the amount of typhoid fever due to the use of raw 
shellfish is not very great, this danger ought to be eliminated 
entirely, and state boards of health should have the authority 
to forbid the sale of shellfish from polluted waters. 

Crawfish and Typhoid Fever. — Dr. Bissell of Buffalo 
wrote to me about an interesting local outbreak of typhoid 
fever which was at first suspected to be due to milk. But 
further investigation showed that it was confined chiefly to 
boys, and that these boys were in the habit of catching craw- 
fish from a lake grossly polluted with sewage. After par- 
tially cooking the crawfish before an open fire in the field, 
the boys would eat them. 

Infection by Fried Fish. 

In 1900, Hamer l of London reported outbreaks of typhoid 
fever in Southwark, Lambert and Kensal-town which seemed 
to be confined in each case to the customers of certain fried- 
fish shops. While the sickness was believed to be due to 
the eating of fish, no conclusion was reached as to how the 
fish became infected. It is scarcely possible that infection of 
the fish before cooking should not be destroyed by the pro- 
cess, and yet it seems unlikely that handling by carriers after 
infection could cause such an outbreak. 

Infection by Watercress. 

In the summer of 1903 there was a very considerable out- 
break of typhoid fever in Hackney, London. 2 This was very 
carefully investigated by Warry, and he eliminated all articles 
of food and drink as sources of the infection, except water- 
cress. Of the 110 cases 55.3 per cent ate watercress which 

1 Hamer, Special Rep. to Med. Off. Health, Lond., 1900. 

2 Warry, Rep. Med. Off. Health, Lond., 1903, 35. 



INFECTION BY FOOD AND DRINK 319 

grew in sewage-polluted water. An inquiry showed that the 
incidence of the disease on watercress eaters was three times 
as great as upon those who did not eat it. 

Infection by Celery. 

Morse 1 reports an outbreak of typhoid fever due to the 
use of celery. There were 49 cases in an insane asylum. 
Nearly all of these belonged to the class of pay patients, to 
whom alone celery was served. Several other persons, how- 
ever, had access to the celery and contracted the disease. 
There were no cases except four contact cases among non- 
users of celery. There had been typhoid fever in the insti- 
tution some months before and the celery bed had received 
the hospital sewage. The disease developed soon after the 
celery came into use. 

1 Morse, Rep. St. Bd. Health, Mass., 1899, 761. 



CHAPTER VIII. 

INFECTION BY INSECTS. 

Importance of Subject. — The subject-matter of this chap- 
ter is of the utmost importance in the practical work of pre- 
ventive medicine, and it is of equal interest to the student of 
scientific epidemiology. Our actual knowledge of the insect 
carriers of disease has all been acquired during the last fif- 
teen or twenty years, and marks as brilliant and successful 
an epoch in the history of medicine as did the phenome- 
nal development of bacteriology in the years immediately 
preceding. 

I hesitate very much to discuss the subject at all, as most 
of the diseases considered are essentially tropical, and of 
tropical diseases I have had no personal knowledge. But 
even we who dwell in temperate regions are likely to meet 
with isolated cases of tropical diseases, or to suffer from 
occasional invasions of yellow fever, bubonic plague and 
relapsing fever. In any event, it is important that both the 
student of preventive medicine and the health officer keep 
informed as to current progress in this line of research, and 
ever bear in mind the possibility that insects may play a 
part, at least, in the spread of those diseases with which he 
is more familiar. 

Modes of Transmission. — There are various ways in 
which disease may be transmitted by insects. The most 
interesting and to us novel manner in which this happens is 
that the discovery of which we owe to Theobold Smith, in 
which the insect, as well as the higher animal, serves as the 
true host of the pathogenic organism which causes the disease. 
Most of the diseases transmitted in this way are probably 
caused by animal parasites, usually protozoa. As a rule, 

320 



INFECTION BY INSECTS 321 

they propagate asexually only in man or the higher animals, 
but develop sexual forms in insects, which thus become, zoo- 
logically considered, their true hosts, while man, if it be a 
human disease, is the intermediate host. The insects in such 
instances are sometimes called biological carriers. In other 
cases the parasites do not develop in the insect, which is then 
merely a mechanical carrier, as would be a lancet or a hypo- 
dermic syringe. The classification of insect-borne diseases is 
far from definite, owing to the present fragmentary condition 
of our knowledge. We will first consider those diseases which 
appear to be biologically carried by insects. 

First Proof of Transmission by Insects. — Although there 
had previously been suggestions that disease might be trans- 
mitted by insects, the first definite proof was the demonstra- 
tion in 1893 by Smith and Kilborne l of the development of 
Piroplasma bigeminum and the part played by ticks in the 
transmission of Texas cattle fever. This discovery did much 
to point out the lines on which experimental work should 
proceed. These authors demonstrated the presence of the 
Piroplasma in the blood of infected cattle and in the ticks 
which fed upon them. They also showed that the ticks trans- 
mit the germ through their eggs to their progeny. The 
new generation of infected ticks then become attached to 
cattle, and by their bites inoculate them and cause the disease. 
It was demonstrated that there could be no infection of the 
fields or fodder, either by the excreta of cattle or by dead 
ticks or ova. The living tick is necessary for the transmis- 
sion of the disease, and doubtless the Piroplasma passes 
through definite phases of its development in the body of the 
tick. Smith and Kilborne showed not only that ticks trans- 
mit this disease, but also that it is transmitted only in this 
way. They furthermore showed that apparently healthy cat- 
tle might be carriers of the Piroplasma, and therefore in the 
presence of ticks could cause the spread of the disease. Texas 

1 Smith and Kilborne, U. S. Dept. Agric, Bu. An. Ind., Bull. 1, 
1893. 



322 THE SOURCES AND MODES OF INFECTION 

cattle fever, though of immense economic importance in the 
cattle-raising industry, is not transmissible to human beings. 
The great importance of Smith and Kilborne's discovery, from 
our present point of view, is the encouragement it gave to the 
study of the transmission of human diseases by insect agen- 
cies. Koch has demonstrated a similar connection between 
ticks and a disease of cattle in German East Africa caused by 
another species of Piroplasma, — P. parvum. Nuttall and 
Graham-Smith x have investigated a similar disease in dogs, 
also transmitted by ticks, and have described the devel- 
opment of the parasite P. canis. Christophers also 2 has 
studied the development of this parasite. There appears 
to be no doubt that piroplasmosis of horses and sheep is 
transmitted by ticks. 

Malaria. 

Discovery of Insect Transmission. — While Nott, 3 King, 4 
Laveran, Koch and others had suggested, on epidemiological 
grounds, that this disease might be insect borne, it was not 
until 1895 that Ross, 6 stimulated by the work of Manson 
on filariasis, watched the development of the malarial parasite 
in mosquitoes which had been allowed to bite persons sick 
with the disease. As Manson had already shown that in 
filariasis it is only a particular species of mosquito which 
can serve as host for the filaria, Ross suspected that the 
same might be true of human malaria, and he finally deter- 
mined that it was only in individuals of the genus Anopheles 
that the malarial parasite can develop. Ross 7 now turned 

1 Nuttall and Graham-Smith, J. Hyg., Cambridge, 1904, 1905, 1906, 
1907. 

2 Christophers, Brit. M. J., Lond., 1907, II, 1333. 

3 Nott, N. Orl. M. & S. J., 1847-48, IV, 563. 

4 King, Tr. Philos. Soc, Wash., 1883. 

5 Laveran, Le Paludisme, Paris, 1891, 147. 

6 Ross, Abst. by Manson, Lancet, Lond., 1896, I, 831. 

7 Ross, Rep. on the Cultivation of Proteosoma Labbe in Grey Mos- 
quitoes, Indian M. Gaz., Calcutta, 1898, XXXIII, 133, 401, 448. 



INFECTION BY INSECTS 323 

to the study of the malaria of birds due to a Proteosoma, and 
he demonstrated that the disease, could be transmitted from 
bird to bird by the bites of mosquitoes. The parasites of the 
disease are taken up with the blood by the insect in the act 
of biting, and after undergoing sexual multiplication, spread 
through the insect, and are found in the salivary gland, 
whence they are injected into the next bird bitten. Mean- 
while Grassi in Italy had come to the conclusion, from a study 
of the distribution of different species of mosquitoes, that 
Anopheles was one of the forms likely to transmit the disease. 
Bignami had previously been unsuccessful in transmitting 
malaria by the bites of mosquitoes, chiefly because he experi- 
mented largely with Culex instead of Anopheles. Finally 
Grassi, Bignami and Bastianelli in 1899 caused malaria in 
human beings by allowing anopheles mosquitoes to bite them 
some days after they had bitten other individuals sick with 
malaria. To avoid the criticism that these experiments were 
carried on in Italy, an intensely malarial country, where 
natural infection could not be absolutely excluded, Patrick 
Manson x had a number of infected mosquitoes sent from 
Italy to England in 1900, and caused two men, Dr. Thurburn 
Manson and Mr. Warren, who had never been in a malarial 
region, to be bitten. Both men developed malaria in exactly 
eighteen days. In the same year Sambon and Low lived for 
three months in the most malarial section of the Roman 
Campagna, protecting themselves absolutely against the bites 
of mosquitoes, but taking no other precautions. They did 
not contract malaria, but of fifteen or sixteen police sent from 
Rome, who spent one night unprotected in the same place, 
every one developed the disease. 2 

Mosquito Sole Carrier of Malaria. — The observations 
and experiments above noted prove conclusively that malaria 
is transmitted by the bites of infected anopheles mosquitoes, 
but do not indicate whether or not it may be spread in other 

1 Patrick Manson, Brit. M. J., Lond., 1900, II, 949. 

2 Sambon and Low, Brit. M. J., Lond., 1900, II, 1679. 



324 THE SOURCES AND MODES OF INFECTION 

ways. It was Manon's theory at first that the malarial para- 
site is transmitted from adult to larvae by means of the water 
in which the eggs are laid, and that this water is also the 
means of infecting human beings. He suggested that germs 
might be inhaled in dust from dried-up and infected pools. 
As regards transmission by water the experiments of Celli l 
and others have already been referred to, which indicate that 
such a mode of transference is highly improbable, and there 
is certainly no epidemiological evidence in its favor. That 
the Plasmodium of malaria grows outside of the animal body 
is also improbable, for it has never been possible as yet to 
cultivate it in any way. 2 It has never been found in the water 
of malarial regions. 3 Even if there are sporelike forms resist- 
ant to drying, there is strong evidence that such are not air- 
borne, for mosquito netting would in no way interfere with the 
free movement of particles small enough to be wafted by the 
air; but abundant evidence has shown that efficient screening 
against mosquitoes affords complete protection against this 
disease, even in the most intensely malarial regions. More- 
over the success attending methods of prevention based on 
the mosquito theory point indubitably to the truth of the 
theory. Experimental, clinical and epidemiological evidence 
combine to demonstrate that malaria is a disease transmitted 
solely by the bites of infected mosquitoes. There are several 
forms of malarial fever, such as tertian, quartan, aestivo-au- 
tumnal, apparently caused by different species of Plasmo- 
dium, but there is no need here of considering these different 
forms and their relation one to another. Suffice it to sa}^ that 
the mosquito appears to be the true host of this parasite, and 
in its body it undergoes sexual reproduction. From eight to 
ten days after the mosquito is infected, its entire body, in- 
cluding its salivary gland, becomes infested with the so-called 
sporozoite forms, and when these are injected into human be- 

1 See chapter on Infection by Water. 

2 Craig, The Malarial Fevers, New York, 1909, 93. 

3 Craig, idem, 83. 



INFECTION BY INSECTS 325 

ings they continue to undergo a vegetative or asexual prolifera- 
tion, the successive phases of which give rise to the symptoms 
of the disease. It is believed that no vertebrate other than 
man serves as the host of the Plasmodium, and until recentty 
it was thought that no mosquitoes except those belonging to 
the genus Anopheles could transmit the disease; but recent 
observations in the Philippines l indicate that a mosquito 
breeding in salt marshes, Myzomyia ludlowii, may become the 
host of the Plasmodium. But it is certain that almost always 
it is some species of Anopheles which is the carrier. Not all 
Anopheles, however, can serve as the host, for one of our 
common species in the northern United States, A. puncti- 
pennis, does not. 2 

Habits of Mosquitoes. — Mosquitoes develop only in water. 
The larval and pupal stages may occupy from eight days to a 
number of weeks, or the larva? may even live all winter 
under the ice in northern regions, or retain their vitality for 
some time in the dried mud of the tropics. The mature 
insects usually live only a few weeks, but in northern regions 
hibernate during cold weather. The habits of life of the dif- 
ferent species of Anopheles vary considerably, and should be 
carefully studied when measures for extermination are under- 
taken. Only the adult female bites, so she alone is the carrier 
of the disease. Anopheles usually bite at night. Gorgas 3 states 
that they do not usually fly above 100 yards, and that clearing 
and draining the area within this distance of houses affords 
great protection. Nevertheless it sometimes happens that 
under favorable conditions the insects may be carried a con- 
siderable distance by the wind. Craig 4 states that they may 
be borne even two and one-half miles. 

Must be Many Mosquitoes. — Mosquitoes are not infected 
with the malarial parasite unless they bite infected human 

1 Banks, Philippine J. Sc. [B. Med.], 1908, III, 335. 

8 Hirschberg, Johns Hopkins Hosp. Bull., Bait., 1904, XV, 53. 

3 Gorgas, J. Am. M. Ass., Chicago, 1909, LII, 1967. 

* Craig, The Malarial Fevers, New York, 1909, 69. 



326 THE SOURCES AND MODES OF INFECTION 

beings. The number of infected mosquitoes, then, varies with 
the number of infected persons to whom they have access. 
Craig l refers to the findings of himself and others as varying 
from 35 per cent to 0.6 per cent. For the spread of malaria it 
is necessary that there should be Anopheles and human beings 
infected with the parasites. But if the mosquitoes are not 
numerous and the cases of infection are not numerous, the 
chances of a mosquito becoming infected and then biting 
another victim after a proper interval are not great, so that it 
may happen that there may be mosquitoes and human infec- 
tion without extension of the disease. Thus it is not known 
that cases of malaria have ever developed on the island of 
Rhode Island, but I have found a few A nopheles breeding there, 
and with the great numbers of summer visitors from all over 
the world, and many soldiers, and sailors of the navy, it is 
probable that the malarial parasite is frequently present on 
the island. These epidemiological facts led me for some time 
to suspect that the supposed mode of transmission of this 
disease above outlined did not contain the whole truth; but 
the directness and strength of the experimental proof, and, 
above all, the success of mosquito control in checking the 
disease render it certain that practically the only way in 
which malarial disease is caused is by the bites of mosquitoes. 
There are numberless interesting details connected with the 
life history and habits of the mosquito which are of great 
importance but which cannot be considered here. The way 
in which these habits explain the peculiarities in the develop- 
ment of malaria is well considered by Nuttall. 2 

Ways of Prevention. — There are several ways in which 
the spread of malarial disease may be checked. 

First. Quinia. — The administration of the various salts of 
quinia prevents the development of the malarial parasite in 
the blood, and this drug is an extremely valuable remedy in 
the prevention and cure of malaria. Antitoxin and vaccines 

1 Craig, loc. cit., 74. 

» Nuttall, Johns Hopkins Hosp, Rep,, Bait., 1899, VIII, 78, 



INFECTION BY INSECTS 327 

are of great value in the prevention and cure of certain of the 
infectious diseases, as diphtheria, typhoid fever and cholera, 
but they are of value chiefly to the individual. The difficulties 
attendant upon their administration are so great that they 
cannot be used except in rare instances to protect large bodies 
of people. The antitoxins, too, probably do not prevent the 
growth of the germs which are the cause of the disease, so 
that in a way their use, as for instance that of diphtheria 
antitoxin, may actually in some instances favor the spread of 
the disease, by preventing the development of symptoms 
when the bacilli are present, thus making a "carrier" instead 
of a "case," and carriers are always difficult to control. It is 
otherwise with quinia. This drug actually kills the Plas- 
modium or drives it out of the circulation and out of the 
way of the mosquito, and so not only protects the individual 
but prevents him from becoming a focus of infection. Quinia 
is not only universally used as a specific curative agent, but it 
is also employed in large quantities as a prophylactic, and its 
employment in this manner is considered a valuable means of 
fighting the disease, reducing as it does the number of foci of 
infection. Indeed Koch and some others claim that this is 
the only way in which malaria can be eradicated, as mosquito 
destruction is in many places impossible. All workers in this 
field employ quinia for this purpose, though there is con- 
siderable discussion as to its mode of administration, which 
varies from 15 grains every eight days, as used by Koch, to 
3 grains daily, as advised by Gorgas. This subject is fully 
discussed by Craig, 1 who states that in the vast majority of 
instances 2\ grains (0.15 grm.) daily is sufficient to prevent 
malarial infection. It is difficult to estimate the value of a 
particular prophylactic measure, for one measure is rarely 
used alone, but there is little doubt of the great efficiency of 
quinia in the fight against malaria. Craig states that at 
Camp Stotsenburg, in the Philippines, measures directed 
against mosquitoes had little result until supplemented by 
1 Craig, The Malarial Fevers, New York, 1909, 343. 



328 THE SOURCES AND MODES OF INFECTION 

the daily administration of quinia. Koch and his followers 
also report excellent results from the use of quinia alone. 
Celli, 1 while urging every method directed against the mos- 
quito, considers that in Italy experience has shown that the 
daily administration of quinia has been the most effective 
measure in reducing the number of deaths from malaria, 
which have fallen steadily from 13,861 in 1901 to 4871 in 1906, 
during which year 20,723 kilos of quinia were sold. 

Second. Isolation of Persons. — The attempt may be 
made to isolate the infected persons so that the mosquitoes 
may not pass from them to the healthy. This may be accom- 
plished in various ways. In many tropical regions where 
the native population, or at least the native children, are 
always infected, the dwellings of the natives and the sus- 
ceptible Europeans are separated a sufficient distance to 
escape the ordinary excursions of the mosquitoes. 

Sometimes the patients, if few in number, are screened from 
mosquitoes in their own homes or are removed to screened 
hospitals. This is very commonly done with the imported 
cases which come to Havana, 2 and in Panama many malarial 
patients are treated in the screened hospitals. Others are 
cared for in their own well-screened houses. 

To assist in this measure it is desirable to kill all mosquitoes 
in the house which may have bitten the patient before the 
disease was recognized or reported to the authorities. Gor- 
gas considers sulphur dioxid the best for this, but as this 
cannot be used in an occupied room, pyrethrum may be 
burned, which so stupefies the insects that they may be easily 
swept up from the floor. Celli has given much study to this 
class of culicides and recommends one or two tablespoonfuls 
of a mixture of the unexpanded flowers of chrysanthemum 
and valerian root. 

Third. Screening. — Effort should be made in all malarious 
regions to protect susceptible persons from the bites of mos- 

1 Quoted by Craig, The Malarial Fevers, New York, 1909, 345. 
8 Guiteras, J. Am. M, Ass., Chicago, 1909, LIII, 1165. 



INFECTION BY INSECTS 329 

quitoes. The screening of the whole house is the most impor- 
tant step. Copper netting is the cheapest in the end, and it 
should, according to Craig, have 11 meshes to 2 cm. Gorgas 
says that it is necessary that houses should be screened by 
persons experienced in mosquito work, or openings are sure 
to be left. The experiments of Sambon and Low proved the 
efficacy of this method of prophylaxis, and Craig states that 
the screening of the houses of railway employees on certain 
Italian lines has been as effectual a method as the administra- 
tion of quinia. Screening is carried on most extensively in 
the Canal Zone. Craig says that where screening is impos- 
sible the use of mosquito canopies over the beds at night is 
a very useful measure, and head nets and gloves for men 
obliged to be out at night are of much value. By the use of 
these methods the percentage of malaria among troops in 
Sardinia was reduced from 70 to 20, and in Formosa no mala- 
ria developed among 115 soldiers protected by netting, while 
of 717 not so protected 251 were attacked. 

The removal of trees, vines and shrubs from the vicinity 
of dwellings is considered by Gorgas an important measure, 
as these serve as hiding places for the insects by day. 1 

A certain amount of protection may be secured by the 
application to the skin of substances annoying to the mos- 
quito, or of ointment which mechanically interferes with 
biting. Oil of citronella or eucalyptus, and petroleum or 
cocoanut oil or vaseline, are used, but such applications 
are not by most writers considered of much value. 

Fourth. Mosquito Prevention. — Theoretically the most 
effectual way to eradicate malaria is to prevent the growth of 
mosquitoes. While their complete destruction is not usually 
possible, its attempt must always take first rank in preventive 
measures. The fact that mosquitoes are a great nuisance, 
as well as carriers of disease, makes still more desirable their 
extermination wherever possible. Large sums, in certain 
parts of the United States, are being expended in fighting the 
1 Gorgas, J. Am. M. Ass., Chicago, 1909, LII, 1967. 



330 THE SOURCES AND MODES OF INFECTION 

salt-marsh mosquito, which is harmless so far as carrying 
disease is concerned. 

Fifth. Draining. — When mosquitoes breed in pools and 
swamps, as they so often do, draining and filling must be 
done. If water cannot be entirely gotten rid of, the banks of 
streams, ponds and ditches must be straightened and deepened, 
and freed from vegetation, to remove hiding places for the 
larvae and permit their destruction. Gorgas insists upon the 
importance of having this work done by men especially trained 
for it, and supervised by experts. Ordinary contractors and 
laborers are sure to overlook breeding places and to neglect im- 
portant details of the work. Many species of Anopheles breed 
in cisterns or accidental receptacles of water near houses. 
Hence all such should either be removed or carefully screened. 

Sixth. Oiling. — The growth of larvae in water can be pre- 
vented by the application of crude petroleum or kerosene to 
the surface at the rate of an ounce to each 15 square feet of sur- 
face. Various poisonous substances may be added to the water, 
as hydrochloric acid, corrosive sublimate, formalin, chloride 
of lime and various aniline dyes. Some of the last named 
are strongly recommended by Celli,as they are harmless to the 
higher animals. The use of quicklime causes a glaze on the 
surface which is a protection, and sulphate of copper kills the 
algae on which the mosquitoes live. Most fish are voracious 
feeders on the larvae, and if pools and streams are supplied 
with fish, and kept free from weeds, mosquitoes cannot thrive. 
It is said that the introduction of a certain small fish into 
the streams of Barbados caused the extermination of mos- 
quitoes. 1 According to Craig, the application of cultures of 
Aspergillus niger and A. glaucus destroys the larvae. 

Success of Measures. — There is probably scarcely a 
locality in which the application of a single prophylactic 
measure will be found effectual in " stamping out " malaria, 
and sometimes all methods combined fail to bring success. 
Thus at Mian Mir in India, according to Craig, the most 
. » Ballou, Nature, Lond., 1909, LXXX, 16. 



INFECTION BY INSECTS 331 

careful draining and oiling were followed by very discourag- 
ing results. On the other hand, preventive measures have in 
many localities given wonderfully good results. The success 
of the work in Italy, as reported by Celli, has already been 
referred to. In Havana the deaths from malaria previous 
to the occupation by the United States averaged 350 per 
annum, rising to 1907 in 1898. The measures carried out by 
Gorgas to destroy the yellow-fever mosquitoes also practi- 
cally eliminated the Anopheles, and the deaths now average 
only about 40, and three-fourths of these are, according to 
Kean, 1 due to infection contracted elsewhere. At Ismailia 2 
the cases were reduced from 2284 in 1900 to 37 in 1905, 
chiefly by destroying the breeding places of mosquitoes. At 
Klang and Port Swettenham in the Federated Malay States 
99 per cent of the mosquitoes were eliminated, with a corre- 
sponding decrease in malaria. Ross also refers to the success- 
ful reduction of malaria at Port Said, Durban, Hong Kong, 
Khartoum, and in Candia, St. Lucia, Greece and Algeria. 3 

Success in Panama. — To my mind the most wonderful 
success of all has been attained by Gorgas in the Panama 
Canal Zone. Here was a stretch of territory 45 miles long, 
intensely malarious, nowoccupied by a force of 44,000 persons, 
mostly foreigners. The rainfall is heavy, and the work of 
canal building alters in every direction the configuration of 
the land and the natural drainage. Malaria caused enor- 
mous losses during the French occupation and was second 
only to yellow fever in interrupting the work. Mosquitoes 
have been entirely eliminated from Colon, a town of 15,000 
inhabitants, and the death rate from malaria among employ- 
ees was only 1.34 per thousand in 1908, having been reduced 
from 5.57 in 1905. Considering the tremendous obstacles to 
be overcome, this success is certainly astonishing. 4 

1 Kean, J. Am. M. Ass., 1909, LIII, 1166. * 

2 Ross, Lancet, Lond., 1907, II, 879. 

3 Ross, Nature, Lond., 1909, LXXX, 415. 

< Gorgas, J. Am. M. Ass., Chicago 1909, LII, 1967. 



332 THE SOURCES AND MODES OF INFECTION 



Yellow Fever. 

History of Discovery. — Nott appears to have been the 
first (1848) to attribute to mosquitoes a role in the causation 
of yellow fever, but this was merely a suggestion which re- 
ceived little attention. According to Cruz, 1 Beauperthuy 
published on the 23d of May, 1854, in the Official Gazette of 
Cumana, Venezuela, an article which expounded with great 
clearness a mosquito theory of this disease. But to Finlay 
of Havana is due the credit for the first experimental work, a 
report of which was presented to the Royal Academy of Medi- 
cal, Physical and Natural Sciences in Havana in 1882. Finlay 
continued to experiment and write until 1900, when the 
American Commission, consisting of Reed, Carroll, Agra- 
monte and Lazear, undertook their investigations at Havana. 2 
Finlay had come to the conclusion that Culex fasciatus, now 
Stegomyia calopus, was the species of mosquito which was 
likely to be involved in the transmission of the disease. After 
the occupation of Cuba by the United States in 1898, the 
war department undertook with great energy the extirpation 
of yellow fever from Havana. At that time the disease was 
believed to be essentially a filth disease, and the energy of 
the government was directed towards making Havana clean, 
and soon its " sanitary condition" vied with that of the very 
best cities in the United States. At the same time the most 
stringent measures of isolation, as isolation was at that time 
understood, were applied. But yellow fever refused to be 
stamped out, and in 1900 caused 1244 cases and 310 deaths, 
many of them among the " best people " in the cleanest parts 
of the city. 3 It was becoming evident that the old theories 
were not satisfactory, and the war department appointed the 

1 Cruz, U. S. Pub. Health & Mar. Hosp. Serv., Pub. Health Rep., 
Wash., 1909, XXIV, 1741. 

2 Lee, Am. Pub. Health Ass. Rep., 1905, XXX, 8. 

3 Series 4, Yellow Fever Pub., San. Dept., Havana, 1902, 10. 



INFECTION BY INSECTS 333 

commission above referred to, which proceeded to Havana 
and in its earliest work put Finlay's mosquito theory to the 
test. They were not a little influenced to this step by the 
observations of Carter. 1 He had determined, from a study 
of the disease in isolated farmhouses, that from nine to six- 
teen days usually elapse, after the introduction of the disease, 
before the house can infect second cases. It was thought 
that this interval might depend upon a period of incubation 
in the mosquito. Owing to the hearty cooperation of General 
Wood, the governor, himself a medical man, every facility 
was accorded the commission, and inoculation experiments 
were made on volunteer human subjects, among whom was 
Lazear, a member of the commission. Of 11 persons bitten 
by mosquitoes which had some days before been allowed to 
feed on a yellow-fever patient, 2 developed the disease, one 
of whom was Lazear, who died as the result of the inoculation. 2 
Carroll too was bitten and developed the disease. As critics 
suggested that natural infection could not be excluded, the 
experiments were repeated in November and December, 
1900, under more convincing conditions, and 6 of 7 persons 
bitten developed typical yellow fever, and the transmission 
of the disease in this manner was demonstrated beyond ques- 
tion. 3 Later Guiteras 4 succeeded in inoculating 8 more per- 
sons, which made a total of 24 persons infected by the bites 
of mosquitoes. Of these 3 died, and the post-mortem ex- 
amination demonstrated the lesions of yellow fever. The 
commission had by the direct transfer of blood shown that 
the infective agent exists in that fluid, even when filtered. 5 
All the experimenters demonstrated that the mosquito could 
not transmit the disease until six to eighteen days after 

1 New Orleans M. & S. J., 1900, LII, 617. 

2 Am. Pub. Health Ass. Rep., 1900, XXVI, 37; Phila. M. J., 1900, 
VI, 790. 

3 Series 3, Yellow Fever Pub., San. Dept., Havana, 1902. 

4 Series 6, Yellow Fever Pub., San. Dept., Havana, 1902, 26. 

5 Am. Med., Phila., 1902, III, 301. 



334 THE SOURCES AND MODES OF INFECTION 

biting a yellow-fever patient, thus explaining the wonder- 
fully accurate clinical observations of Carter. Although it 
has been shown that filtered blood contains the infective 
principle, thus far it has not been demonstrated by micro- 
scopical or cultural methods. It seems in the highest degree 
probable, from this very remarkable work, that the exciting 
agent of yellow fever closely resembles that of malaria, in 
that it is found in the blood, is taken up by a particular 
species of mosquito, develops in the mosquito during a period 
of some days, and is then transmitted to new subjects only 
by the subsequent bites of the insect. 

Transmission by Fomites Disproved. — Belief in the infec- 
tiousness of the vomitus and excreta and in the important 
part played by fomites in the extension of the disease was 
so firmly fixed that it seemed necessary to test this theory 
by actual experiment. The commission for this purpose 
exposed a number of non-immune persons to the closest 
possible contact, during a period of two weeks, to bedding, 
clothing and other articles all grossly contaminated with 
supposedly infective material, but none of them contracted 
the disease. Later Guiteras, while carrying on his mosquito in- 
oculations, incidentally exposed many non-immunes to fabrics 
that had been in close touch with yellow-fever cases, but with 
like negative results ; and again Gorgas, at Las Animas Hos- 
pital in Havana, put the fomites theory to test in the most 
thorough manner by the exposure of non-immunes to close 
and continued contact. 1 

Even before these demonstrations, some acute observers, 
especially Carter, 2 had concluded from epidemiological studies 
that fomites played little part in the dissemination of this 
disease. Carter showed among other things that countless 
pieces of baggage, many of them certainly from infected 
houses in Cuba and Vera Cruz, had passed to northern ports 
without causing yellow fever in a single instance. 

1 Series 3, Yellow Fever Pub., San. Dept., Havana, 1902, 22. 
" Carter, Med. News, N. Y., 1904, LXXXV, 878. 



INFECTION BY INSECTS 335 

Transportation of Mosquitoes. — Theoretically there is no 
reason why infected mosquitoes might not occasionally be 
carried in baggage, but admission of baggage without dis- 
infection, without any known instance of the development of 
yellow fever, shows that such a mode of transmission must 
be extremely rare. Even the carriage of infected mosquitoes 
in vessels must be unusual, though instances are recorded by 
Carter ' and others. Grubbs 2 found Stegomyia calopus on 
three of sixty-five vessels entering the Gulf Quarantine Sta- 
tion. Souchon, 3 at New Orleans, found that 2.5 per cent of 
the mosquitoes caught on incoming steamers from Havana 
or the West Indies were Stegomyia calopus. Probably none 
of these were infected. 

The rapid and brilliant demonstration of the true mode of 
extension of yellow fever was immediately followed by an 
equally rapid and brilliant application of the new knowledge. 
Two months after the termination of the commission's ex- 
periments, Gorgas was as energetically applying the new 
methods of yellow-fever control in Havana as he had pre- 
viously devoted himself to cleansing the city, and within 
eight months the Stegomyia calopus had been nearly exter-» 
minated, and Havana was free from the disease for the first 
time in 150 years. 

Habits of Yellow-fever Mosquito. — Different species of 
mosquitoes have different habits of life, and Stegomyia calopus 
is much more of a domestic mosquito than are the Anopheles. 
It prefers to breed in clean rain water, but will grow in any 
water that is not too muddy. It may even be found in cess- 
pools and in gutters, but its favorite home is the rain-water 
cistern, barrel, jar or other container which is usually pro- 
vided for every house. It seems to prefer dark, covered recep- 
tacles. The adult mosquito is rather feeble and rarely flies far. 

1 Carter, Med. Rec, N. Y., 1902, LXI, 441. 

2 Grubbs, Yellow Fever Institute, U. S. Pub. Health & Mar. Hosp. 
Serv., Bull. No. 11. 

1 Souchon, J. Am. M. Ass., Chicago, 1903, XL, 1647. 



336 THE SOURCES AND MODES OF INFECTION 

Preventive Measures. — The defensive measures against 
yellow fever must of course be somewhat like those directed 
against malaria, but differ in some important particulars. 
The most important of these is that there is no drug which 
will prevent and cure this disease as quinia does malaria. 
Another point of difference is that yellow fever is not nearly 
so widespread a disease as is malaria, and that it is an acute 
disease in which the patient remains infectious for only a 
short time. Among the measures directed against yellow 
fever are: 

First. Quarantine. — While inland quarantine has never 
been successfully administered, maritime quarantine for 
yellow fever is certainly of value. The short period of 
incubation of the disease, the absence of chronic cases 
and the fact that it prevails in endemic form in only a 
few places which are in communication with the rest of 
the world chiefly by water, render it possible to intercept 
at the port of debarkation a goodly number of incom- 
ing cases. Quarantine, while often failing, has many times 
proved its value in the United States; and in Havana, after 
the disease was exterminated, it would certainly have many 
times been introduced from Vera Cruz and Colon, and indeed 
probably from New Orleans, if the careful inspection of 
incoming passengers had not been maintained by the depart- 
ment of health. The efficiency of quarantine is greatly 
increased if an agent is stationed at the port of embarkation, 
as is done at many ports by the United States Public Health 
Service. 

Second. Screening of Cases. — Extraordinary effort must 
be made to get control of every case of the disease. The 
diagnosis is not always easy, and able diagnosticians must 
be employed. In the Canal Zone a prize of $100 is offered 
for the discovery of a case of yellow fever. The harsh treat- 
ment formerly accorded these cases, the injury to property 
caused by disinfection, and the tremendous* loss to business 
by the old methods of quarantine, put a premium on con- 



INFECTION BY INSECTS C37 

cealment; but there is much less tendency to hide cases now 
than formerly. When reported, the case is protected from 
mosquitoes either by efficient screening or, as is now usually 
done in Havana and the Canal Zone, by removing the patient 
to a well-screened hospital. 

Third. Destruction of Mosquitoes. — Infected mosquitoes 
in the house occupied by the patient and in neighboring 
houses must be destroyed. Sulphur dioxid is the best culi- 
cide for this purpose, but pyrethrum powder may be burned 
while the room is occupied and the stupefied mosquitoes 
swept up, as in malaria. 

Fourth. Prevention of their Growth. — The most impor- 
tant means of preventing yellow fever is to reduce the number 
of stegomyia mosquitoes to a minimum by destroying their 
breeding places in the same manner in which the breeding 
places of malarial mosquitoes are destroyed, by draining, fill- 
ing, ditching and the use of petroleum and culicides in the 
water. As the stegomyia so often breeds in domestic recep- 
tacles which in the absence of a municipal water supply and 
sewers cannot be dispensed with, the efficient screening of 
these receptacles is an important part of sanitary work in 
the American tropics, and constant inspection is needed to 
see that the screening is maintained. 

Success of Measures. — The phenomenal success of these 
measures in Havana has already been referred to, but the 
eradication of the disease in the Canal Zone is a still more 
remarkable achievement. Havana is a compactly built, well- 
drained city, and was under military rule. The Canal Zone 
is about forty-five miles long, with swamps and streams, many 
straggling villages and camps, a heavy rainfall, continuous high 
temperature, a constantly changing non-immune population, 
stupendous engineering works altering the configuration of 
the hind, and a persistenl yellow-fever infection for centuries. 
This disease had been the chief obstacle in the construction 
of the Panama railroad, and it was the chief obstacle to the 
French in their canal work. Their loss by death from this 



338 THE SOURCES AND MODES OF INFECTION 

disease amounted probably to from 12 to 15 per cent per 
annum. 1 Sanitary work began on the isthmus in February, 
1905, at which time yellow-fever cases were being constantly 
reported. The cases soon began to decrease, and within a 
year the disease was practically exterminated. 2 In Rio Ja- 
neiro the campaign against yellow fever began in April, 1903. 
The undertaking was expensive, as it always must be if it is 
to be successful. It required the expenditure of $1,650,000 a 
year and the employment of thirteen hundred men. Deaths 
from yellow fever, which had averaged twelve hundred a 
year for nearly forty years, decreased rapidly, as is shown 
by the following: 

Year. Deaths. 

1903 584 

1904 48 

1905 289 

1906 42 

1907 39 

1908 4 

1909 

In Vera Cruz, which was another stronghold of yellow 
fever, the disease has been almost eradicated by the employ- 
ment of anti-mosquito measures. 3 

Filariasis. 

First Parasite Studied in Insects. — While the infection of 
the blood of man with Filaria bancrofti is in most cases not 
accompanied by noticeable symptoms, it is of interest in this 
connection as being the first infection in which the parasite 
was proved to be taken up into and undergo metamorphosis 
in the body of an insect. This tiny worm is found swimming 

1 Gorgas, J. Am. M. Ass., Chicago, 1909, LIII, 597. 

2 Cruz, Pub. Health Rep., U. S. Pub. Health & Mar. Hosp. Serv., 
Wash., 1909, 1742. 

3 Liceaga, Am. Pub. Health Ass. Rep., 1905, XXXI, 284. 



INFECTION BY INSECTS 339 

in vast numbers in the blood of those who are infected, but 
is found only at night. During the day it disappears from 
the peripheral circulation and is found only in the heart and 
lungs. When these larval forms are sucked up by the mos- 
quito they increase rapidly in size and become more highly 
organized, and working their way to the proboscis of the 
insect, infect the next person bitten. The worms, now pre- 
senting sexual forms, reach the lymph ducts, where the eggs 
are laid and whence the young larvae reach the blood 
current. It is now generally believed that injury to the 
worms in the lymph vessels causes obstruction of the latter 
and the development of tropical elephantiasis. Culex fatigans 
is probably the insect chiefly concerned in the spread of the 
infection. The disease has not been actually transmitted to 
man by the bites of infected mosquitoes, but the develop- 
ment of the worm in the mosquito was observed by Manson 
in 1878 l and by Lewis in 1879. 2 A similar infection in dogs 
has been actually transmitted by means of mosquitoes. 3 

Sleeping Sickness. 

Discovery of Trypanosoma — The trypanosome (T. gam- 
biensis), which is the cause of sleeping sickness, was found 
in the blood of patients by Dutton and Todd in 1901. This 
disease is very widely distributed in Africa, and it is esti- 
mated to have caused over 100,000 deaths in Uganda during 
the six years from 1901-1907. This trypanosome is patho- 
genic for many of the lower animals, and in monkeys causes 
symptoms resembling those produced in man. Bruce and 
Nabarro 4 showed that the disease may be transmitted by 
insects, for in 1903 they succeeded in inoculating a monkey 
by allowing it to be bitten by tsetse flies (Glossina palpalis) 

1 Manson, Med. Times & Gaz., Lond., 1878, II, 731. 

2 Lewis, Quart. J. Micr. Sc, Lond., 1879, XIX, 245. 

3 Braun, The Animal Parasites of Man, 3d ed., New York, 1908, 285. 

4 Bruce and Nabarro, Rep. of Sleeping Sickness Commission, Roy. 
Soc, 1903, No. 1. 



340 THE SOURCES AND MODES OF INFECTION 

which had twenty-four to forty-eight hours previously bitten 
negroes suffering with the disease. While this much has 
been established with certainty, there are important points in 
the causation of the disease which are still under discussion. 

While Glossina palpalis is known to transmit sleeping sick- 
ness, and the distribution of this fly in a large degree corre- 
sponds with the distribution of the disease, it is not certain 
whether it may not be carried by other species of tsetse flies, 
and perhaps by domestic insects and by mosquitoes, 1 and 
Koch 2 thinks it possible that it may be transmitted by the 
sexual act. Comparatively little is known about the breeding 
habits of the fly. 

Does it infect Lower Animals? — There has also been much 
discussion as to whether the specific trypanosome of this 
disease naturally infects the lower animals. If they are gener- 
ally affected, they become a vast reservoir from which the 
trypanosomes may be transferred to human beings by the 
fly, and the difficulties in the way of controlling the disease 
become enormous. Even the crocodile has been suggested 
by Koch as an important " reservoir." But Hodges 3 says 
that actual observation shows that no animal except the 
native dog, and that in only a few instances, has been found 
naturally infected. A cause of the uncertainty is a wide- 
spread distribution of several kinds of trypanosomes not easily 
distinguished from T. gambiensis. 

Is it carried Mechanically? — Another question of impor- 
tance, especially from a scientific standpoint, is whether the 
trypanosome passes through a cycle of development in the 
fly. It was at first supposed that this was the case, but later 
observations, especially those of Minchin, 4 seemed to indicate 
that this was not so. According to his observations flies are 

1 Bull. Soc. path, exot., Par., 1908, I. 

2 Koch, Deutsche med. Wchnschr., 1907, XXXIII, 1889. 

3 Cited in Supl. to Third Rep., Wellcome Research Lab., Khartoum, 
1908, III, 172. 

4 Minchin, Quart. J. Micr. Sc, Lond., 1908, n. s., LII, 159. 



INFECTION BY INSECTS 341 

infective at once after biting a subject, and the power to 
infect does not last over forty-eight hours. More recently, 
however, Bruce l has shown that the parasites do undergo 
developmental changes in the fly, and that flies do not infect 
until from 14 to 20 days have elapsed after feeding on a case. 
Kleine 2 also has demonstrated the same for other forms of 
trypanosomes. It is possible that the trypanosomes may be 
occasionally carried mechanically on the proboscis of the 
tsetse fly, in which case infection will take place at once, 
and also that the parasites pass through certain metamor- 
phoses in the fly, thus permitting the flies to remain infective 
for some time. 

Prevention of Sleeping Sickness. — The measures sug- 
gested for limiting sleeping sickness are: 

First. Quarantine, or the prevention of the entrance of 
infected human beings into regions occupied by the fly. 
While this may be of value at times, it scarcely seems possible 
to an observer at this distance that it can be often employed 
effectually in Africa. 

Second. The sick may be segregated and kept out of 
reach of the flies until the trypanosomes have disappeared 
from the blood. 

Third. The removal of the entire population from the 
area occupied by the fly. The tsetse flies are found only from 
thirty to one hundred yards from water, so that if all settle- 
ments are removed this distance from rivers and lakes much 
will be done to prevent the spread of the disease. 

Fourth. As trees and shrubs afford a hiding place for the 
flies, the thorough clearing of the land around villages and 
near landing places and shore market places has been found 
useful, just as similar clearing has been found to be an impor- 
tant means of controlling malaria in the Canal Zone at 
Panama. 

1 Bruce, Bull, of Sleeping Sickness Bu., 1909, Nos. 6 & 7. 

2 Kleine, Deutsche med. Wchnschr., 1909, XXXV, 924. 



342 THE SOURCES AND MODES OF INFECTION 

Fifth. The administration of atoxyl (anilin meta-arse- 
nate) is believed by many to shorten the life of the parasite 
in the body, and if so, it becomes a valuable prophylactic 
measure, similar to the use of quinia in malarial affections. 

Kala-azar. 

Protozoan Discovered by Leishman. — Kala-azar, or dum- 
dum fever, occurs in various tropical countries, particularly 
in India. It runs a chronic course and is characterized by 
marked enlargement of the spleen. In 1900 Leishman dis- 
covered in splenic pulp, from a case of the disease, certain 
bodies the importance of which he did not appreciate, but 
later, in 1903, he concluded that they might be protozoa. 
The discovery was confirmed the same year by Donovan. 
These bodies are now recognized as protozoa, and are known 
as Leishmania donovani, and are probably the cause of the 
disease. Similar bodies were found by Wright of Boston in 
oriental sore, and by Nicolle and Cassuto in an infantile 
splenic disease in Tunis. Rogers, Patton and others have 
succeeded in growing the parasite in culture medium outside 
of the body, and both have also obtained evidence to show 
that the disease may be transmitted by the bedbug. Both 
Patton and Rogers have shown that a well-defined cycle of 
development takes place in the body of that insect, which 
renders it very probable that it is the intermediate host. 
Patton says, "There is no shadow of doubt that the bed- 
bug transmits the disease," but this has as yet not been 
definitely proved. 1 

Dengue. 

Transmitted by Mosquitoes. — The causation and mode 
of transmission of dengue are somewhat uncertain. Graham 
believes that he has demonstrated in the blood a protozoan 

1 The above is taken chiefly from The Malarial Fevers, Craig, 1909, 
411, and the Supplement to the Third Report of the Wellcome Research 
Laboratories, 1908, 95. 



INFECTION BY INSECTS 343 

which he considers the cause of the disease, but his findings 
have not been substantiated. Ashburn and Craig x demon- 
strated that it is possible to transfer the disease to healthy 
men by the inoculation of blood from the sick, and that the 
virus is contained in the filtered blood. They also proved 
that the disease can be transmitted by a mosquito, Culex 
fatigans, and they consider that this is probably the most 
common mode of transmission. Stitt also believes that the 
mosquito is the bearer of the disease. Carpenter and Sut- 
ton could not transfer the disease by mosquitoes, but they 
did not experiment with C. fatigans. Ross has shown that 
while dengue prevailed elsewhere in Egypt, there was none 
in Port Said and Ismail ia, where the mosquitoes had been 
exterminated. Balfour, 2 from whose review this information 
is chiefly taken, states that in Khartoum, which was com- 
paratively free from mosquitoes, especially C. fatigans, there 
was no dengue, though persons with the disease in all proba- 
bility came there from Port Sudan and Haifa. It appears 
probable, therefore, that the contentions of Ashburn and 
Craig are correct. 

Relapsing Fever. 

Varieties. — According to Craig, 3 there are at least four 
forms of relapsing fever, each due to a particular kind of 
spirocheta, and each apparently limited in geographical dis- 
tribution. It is still uncertain whether these spirochete are 
bacteria, as was formerly believed and as is strongly urged 
by Novy and Knapp, or protozoa, similar to the trypano- 
somes, as is maintained by Schaudinn, Prowazek, Leishman 
and others. Whatever they may be, there is no doubt that 
at least one form of the disease is carried from person to 
person by means of ticks. 

1 Ashburn and Craig, J. Infect. Dis., Chicago, 1907, IV, 440; also 
Philippine J. Sc. [B. Med.], II, 93. 

2 Supplement to the Third Rep., Wellcome Research Lab., Khar- 
toum, 1908, 37. 

8 Craig, The Malarial Fevers, New York, 1909, 445. 



344 THE SOURCES AND MODES OF INFECTION 

Ticks. — The African form of relapsing or tick fever is 
caused by S. duttoni, which was discovered by Dutton and 
Todd, and also by Ross and Milne in 1904, the first named 
of whom, Dutton, lost his life while studying the disease. 
Dutton and Todd demonstrated beyond question that the 
disease may be carried from man to man by a tick, Orniiho- 
dorus moubata, and their observations were confirmed by Ross 
and Milne and by Breinl and Kinghorn. It was also shown 
that the disease is hereditary in ticks, according to Mollers, 1 
even to the second generation. Unlike the malarial parasites 
and the trypanosomes, these spirochete soon disappear from 
the blood, and chronic latent infections do not seem to exist. 
Koch, however, suggests that the spirochete may ultimately 
be found in rats, and that these rodents may be the real 
source of this disease, as they are of plague. The tick, how- 
ever, is said to be exclusively a human parasite. It is found 
in the floors and crevices of houses and native huts, where it 
hides during the day and feeds at night. The spirochete 
undergo a certain development and multiplication in the tick, 
but whether they pass through a definite cycle of develop- 
ment, like the protozoa, is not known. Ticks have been 
known to be infective for a year and a half. 

Bedbugs. — Even before the discovery of the spirocheta it 
was suggested that the bedbug might be the carrier of the dis- 
ease, but, according to Balfour, 2 Breinl and Kinghorn, and 
Todd have by experiment shown that this is probably not so. 

Less is known about the other forms of relapsing fever. 
Tictin in 1897 believed that the recurrent fever of Europe is 
transmitted by the bedbug, and he claimed to have demon- 
strated its possible transmission in this way, but the experi- 
ments were not entirely satisfactory and have not been 
substantiated. 

1 Mollers, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1908, LVIII, 
277. 

2 Supplement to the Third Report, Wellcome Research Lab., 
Khartoum, 1908, 190. 



INFECTION BY INSECTS 345 

The Indian form of the disease is caused by S. carteri, and 
has been much studied. Mackie could demonstrate the spi- 
rochete in bedbugs fed on relapsing-fever patients, up to 
the sixth day, but he found no evidence of their increase. 
Of fifty-three bugs found in a fever ward, only one contained 
spirochete. He also placed infected bedbugs in cages with 
six monkeys, and only one of the monkeys contracted the 
disease. Other sources could not be excluded. 

Lice. — Recently the same author has found the spiro- 
chete in from two to fourteen per cent of body lice found in 
fever wards, and he showed that the parasites increased 
in number in the lice. Sergent and Foley, in Algeria, have 
made observations and experiments tending to implicate the 
clothes louse, Pediculus vestimenti. 

Rocky Mountain Fever. 

Transmitted by Ticks. — Rocky Mountain tick fever prob- 
ably appeared in Idaho about 1885, and is now found in 
Idaho, Montana, Washington, Oregon, Wyoming and Utah. 
It is an acute fibrile disease with a high mortality, usually 
exhibits an eruption on the skin, and is followed by immunity. 
According to the investigations of Ricketts, 1 the disease is 
transmitted by means of ticks, probably from some of the 
small wild animals of the country. He showed that it is 
possible to transmit the disease to monkeys, guinea pigs, 
gophers, chipmunks, rock squirrels and other . animals by 
allowing ticks (Dermacenter andersoni) to bite first an infected 
animal, and later a healthy animal, which soon becomes 
infected.' There is evidence that the virus of the disease 
develops in the body of the tick and is transmitted to its 
offspring. Ricketts has shown by inoculation experiments 
that the virus is contained in the blood serum of infected 
animals, and he recently 2 reports the discovery of a bacillus 
which he believes to be the cause of the disease. 

1 Ricketts, Rep. St. Bd. Health, Idaho, 1907-08, 88. 

2 Ricketts, J. Am. M. Ass., Chicago, 1909, LII, 379. 



346 THE SOURCES AND MODES OF INFECTION 

Biological Carriers Distinguished from Mechanical Carriers. 

— In most of the diseases thus far considered in this chapter 
the parasite which causes the disease passes through a defi- 
nite cycle of its existence in the insect as well as in man. 
The insect is in most cases the true host of the parasite and 
has been called a " biological carrier " of disease. Most of 
the parasites transmitted in this way belong to the protozoa. 
On the other hand, insects may be merely " mechanical 
carriers " of disease. The blood which contains the germs of 
the disease may be carried on the mouth parts of the insect 
and inoculated into the next person bitten, just as it might 
be carried on the point of a lancet. 

Plague. 

Discovery of Bacilli in Fleas. — According to Nuttall, 1 
Ogata in 1897 found plague bacilli in fleas taken from the 
body of a rat dead of bubonic plague, and this observation 
was confirmed by the German Plague Commission the same 
year. In 1898 Simond noted that persons who handle dead 
rats not rarely die of the plague, but he found that infection 
never occurred if the rats had been dead over twenty-four 
hours. He also found that persons with plague occasionally 
presented on their skin what appeared to be flea bites, and 
he was able to demonstrate plague bacilli in these supposed 
bites. He was able also to demonstrate plague bacilli in 
fleas taken from rats dead of the plague. 

Plague derived from Rodents. — Simond's observations 
led to much study and experiment and to still more contro- 
versy. It has been shown by large numbers of observations 
that plague is primarily a disease of the lower animals, par- 
ticularly of rodents, many species of which easily become 
infected. It has been shown also that plague in man is gen- 
erally derived from the same disease in rats, or more rarely 
mice, and recently in California from ground squirrels (Citel- 
lus beecheyi). 

1 Nuttall, Johns Hopkins Hosp. Rep., Bait., 1899, VIII, 1. 



INFECTION BY INSECTS 347 

Epidemiological Evidence. — The very careful observa- 
tions of Thompson 1 in Australia showed that outbreaks of 
human plague were preceded by outbreaks of rat plague, 
that human cases were connected in one way or another with 
foci of rat infection, and that the dispersal of human cases 
did not result in the dispersion of plague. He showed that 
while human plague had a local association with rat plague, 
the association was not a direct one, but was such as to render 
necessary the assumption of some such intermediary as the 
flea. It also seemed to him that the location of the buboes 
was in accord with the theory of flea infection. 

Experimental Work. — Objection had been made by Nut- 
tall and others to the flea theory on the ground that rat and 
human fleas are of different species, but Tidswell in Sydney 2 
showed that rat fleas when hungry will bite man. This has 
been substantiated by many other observers, some of whom 
have also shown that Pulex irritans, the human parasite, will 
occasionally bite rats. It has also been shown that fleas 
speedily leave a dead animal, and then, impelled by hunger, 
they attack the nearest victim. As was shown by Nuttall, 
plague bacilli may live in fleas for several days. The English 
Plague Commission found as many as 5000 bacilli in the 
stomach of a single flea, and they believe that they increase 
in number for a while and sometimes live for fifteen days, 
but in starved fleas do not live over a week. 3 Verjbitski 4 has 
also confirmed these observations. He has shown, too, as did 
Nuttall, that bedbugs may become infected and harbor the 
germs for some days. According to Tidswell, 5 rats are fre- 
quently infested with bedbugs (Cimex lectularius) , but there 
is no evidence as yet that these play any important part in 

1 Thompson, Reports of Plague in Sydney, 1902 to 1907. 

2 Tidswell, Rep. on Second Outbreak of Plague in Sydney, 1902, 
73-75. 

3 J. Hyg., Cambridge, 1907, VII, 419. 

4 Verjbitski, J. Hyg., Cambridge, 1908, VIII, 162. 
6 Loc. cit. 



348 THE SOURCES AND MODES OF INFECTION 

the causation of the disease. Verjbitski showed that if the 
biting insect is crushed on the skin, either the bite or neigh- 
boring scratches are easily infected. 

Demonstrations in India. — Finally, the very beautiful 
experiments of the English Plague Commission 1 showed con- 
clusively that infection by fleas was practically the only way 
in which experimental animals could be infected under natural 
conditions. These experiments have been referred to on 
pages 204 and 262. In one experiment, a plague-infected vil- 
lage was cleared of its human inhabitants and guinea pigs 
placed in the houses, and it was demonstrated that infection 
took place only through the medium of fleas. The experi- 
mental and epidemiological evidence is that the bubonic form 
of human plague, which is by far the most common form, is 
caused by the transference of the bacilli from rodents to man 
by means of fleas. 

Plague rarely spread except by Fleas. — While it is true 
that the flea is the chief agent in the transmission of plague, 
the disease may possibly be, and doubtless occasionally is, 
spread in other ways. In experimental animals it is possible 
to induce it by the ingestion of infected food, and the contact 
of the abraded or injured skin with any substance containing 
plague bacilli may result in infection. The pneumonic form 
of plague, when no precautions are taken, is highly contagious, 
for the sputum contains the bacilli. In some outbreaks of 
plague the pneumonic form prevails. In some localities the 
overcrowding, filth and habits of the people may cause con- 
tact infection or infection by food to assume some impor- 
tance, but in Western Europe, Australia and America there 
can be little doubt that plague is chiefly a flea-borne disease. 

Measures against Plague. — Measures against the plague 
ought, then, to involve the isolation of the sick, particularly 
those sick with the pneumonic form. In India evacuation 

< * J. Hyg., Cambridge, 1906, VI. 

See also Summary of Work of Commission, 1908, Calcutta, Supt. of 
Gov. Printing. 



INFECTION BY INSECTS 349 

of infected villages, that is, the removal of the population 
from the vicinage of the plague rat, is a measure of value. 
Disinfection, if it includes the killing of fleas and rats, is an 
important measure. Haffkine's serum has been found to pre- 
vent attacks for several months, and its general use is often 
of value in preventing the development of individual cases. 
But the chief anti-plague measures must be directed, not 
against the flea, but against rats and other rodents. The most 
obvious procedure is to attempt the destruction of the rats, 
but thus far this has proved to be a rather hopeless under- 
taking. Poisoning, trapping and destruction by infectious 
disease have proved only palliative or adjuvant measures. 
In Japan, in Australia and in California the most energetic 
rat destruction has not materially reduced their numbers. 
Thompson * says : " Prevention of epidemic plague conse- 
quently lies in maintaining a distance between the rat and 
man. The requisite separation between rat and man will be 
better secured by improving the construction of buildings 
than by attempts to exterminate the rat." In Sydney large 
sums are being spent in rebuilding wharves and warehouses 
so as to render them rat-proof. In San Franscisco 2 every 
effort has been made to prevent the growth of rats by cutting 
off their food supply, by improved scavenging, and by pro- 
viding metal garbage pails and rat-proof receptacles for all 
kinds of food and grain likely to attract rats. But the chief 
effort was directed to rat-proofing, by the use of concrete 
construction, of stables, markets, provision and produce ware- 
houses and wharves. 

Anthrax. 

Nuttall, in his valuable discussion and bibliography of the 
subject of insect carriers of disease, 3 cites a large number of 

1 Thompson, Internat. Cong. f. Hyg. u. Demog., Berl., 1907, III, 672. 

2 Eradicating Plague from San Francisco, Rep. of Citizens' Health 
Com., 1909. 

* Nuttall, Johns Hopkins Hosp. Rep., Bait., 1899, VIII, 1; see also 
Rep. to Local Gov. Bd., Lond., on Pub. Health, 1909, n. s., 16. 



350 THE SOURCES AND MODES OF INFECTION 

authors who suggest that anthrax may at times be trans- 
mitted by any biting insects which pass from cattle to man. 
Numerous instances are given of persons who date the begin- 
ning of their pustule from the sharp sting of an insect, but, 
as was well said, it is probable that often the first noticeable 
sensations in the development of the pustule are wrongly 
considered as due to the bite of an insect. In a few cases a 
fly was felt to bite and was killed, and on the spot a ma- 
lignant pustule developed. Most of the score or more of 
writers quoted urge this mode of infection on purely a priori 
grounds, and it is certainly highly probable that where 
anthrax is at all prevalent among animals, and biting insects 
pass from the lower animals to human beings, the disease is 
sometimes transmitted in this way; but, as has been sug- 
gested, if this happened often, the disease would be more 
common than it is. Certainly in England and the United 
States practically all human anthrax results from handling 
infected material. 

Nuttall * allowed bedbugs to suck blood from mice infected 
with anthrax, and then caused them immediately to bite 
healthy mice. In all, 136 infected bugs were used, but in no 
instance did they transmit the disease. In six instances the 
bugs were crushed while biting, but these experiments were, 
like the others, without result. Nuttall also made a few 
similar experiments with fleas, with like negative results. He 
found that anthrax bacilli remained alive in bedbugs only 
for from two to four days, and died off even more quickly 
in fleas. 

Nuttall carried on similar experiments with bedbugs and 
chicken cholera, but these were equally unsuccessful. 

Septic Infection. 

Nuttall cites Faure, Paltauf, Chrzaszczewski, Joseph and 
Berry as having noted instances of septic infection following 
the bites of insects, and others are occasionally noted in medi- 
1 Nuttall, loc. cit., 13. 



INFECTION BY INSECTS 351 

cal literature. That this accident should sometimes happen 
seems very probable. 

Typhoid Fever. 

Dutton 1 caused bedbugs to bite a typhoid-fever patient 
and after twenty-four hours' fasting to bite two other healthy 
persons, both of whom developed typhoid fever in twelve 
and fourteen days respectively. 

Insects carry Germs on Bodies. — The insects thus far 
considered inoculate disease by means of their bites, but it is 
evident that some diseases may be carried by them in other 
ways. If infective material exists in considerable quantity, 
and is accessible to insects, they are almost certain to get it 
on their legs and bodies, and may then carry the germs to 
other human beings. The chance of their doing this varies 
greatly with varying conditions. If the insects fly, the danger 
would seem to be much greater. If the infective material is 
large in amount and freely exposed, as typhoid excreta in 
privy vaults, the danger of fly infection is increased, and it 
is also greater if there is a possibility of infecting food which 
insects love to visit. 

Flies carry Germs. — It is therefore not surprising that 
many persons, even years ago, suggested that insects might 
be the carriers of disease. Nuttall cites many of these. 
With the development of bacteriology, experiments began to 
supplement conjecture, and it was definitely determined that 
bacteria might be carried on the bodies of insects, which 
indeed is self-evident, and also that they might in a living 
state pass through the stomach and be voided in the feces. 
According to Nuttall, Raimbert, Davaine and Ballinger 
demonstrated living anthrax bacilli on flies of various kinds 
that had been feeding on infected material. Nuttall himself 
showed that house flies could carry for forty-eight hours 
living plague bacilli which they had derived from material 
they had fed on, and Hankin showed the same for ants. 
1 Dutton, J. Am. M. Ass., Chicago, 1909, LIII, 1248. 



352 THE SOURCES AND MODES OF INFECTION 

Cholera. — In 1886 Tizzoni and Cattani caught flies in a 
cholera hospital in Bologna and found that cultures made 
from them showed cholera spirilla. Simmonds made similar 
observations in Hamburg in 1892. Macrae in India, in 1894, 
exposed boiled milk in different parts of a jail where cholera 
prevailed, and found that it became infected with cholera 
germs. Tsuzki, in 1904, captured cholera-infected flies in a 
house in Tientsin where there were cases of the disease. 
Chantemesse and Gagnon have shown that flies may carry 
virulent germs for seventeen and twenty-four hours re- 
spectively. Maus l says that cholera spirilla were found on 
several bluebottle flies caught in infected houses in the 
Philippines. 

Typhoid Fever. — Celli fed flies with pure cultures of 
the typhoid bacillus and found that virulent germs passed 
through the intestines. Firth and Horrocks 2 showed that 
typhoid bacilli could be carried on the legs and bodies of 
flies, but they did not prove that they could pass through the 
digestive tract of the insects. Hamilton 3 in Chicago, and 
Fricker in Hamburg, in the same year, recovered typhoid 
bacilli from flies in houses where there were cases of the 
disease. Klein 4 also recovered typhoid bacilli from flies from 
houses where there was typhoid fever. Buchanan 5 did not 
find typhoid bacilli on flies caught in an enteric-fever ward, 
but he found that flies could readily be made to distribute 
typhoid germs over an agar plate. Prof. F. P. Gorham, at 
my request, exposed agar plates in the pantry of a house 
where there were five cases of typhoid fever. The place was 
swarming with flies and the privy was just outside of the 
window. Flies were frequently walking over the plates, but 
no typhoid bacilli were found. Gunn, in Orange, N. J., was 

1 Maus, Abst. Med. News, N. Y., 1902, LXXXI, 318. 

2 Firth and Horrocks, Brit. M. J., Lond., 1902, II, 936. 
8 Hamilton, J. Am. M. Ass., Chicago, 1903, XL, 576. 

4 Klein, Brit. M. J., Lond., 1908, II, 1150. 

6 Buchanan, Abst., Glasgow M. J., 1907, LXVII, 305. 



INFECTION BY INSECTS 353 

similarly unsuccessful. Hewitt 1 allowed flies to walk over 
thin smears of typhoid feces and then kept them in cages 
for 24 hours and after that allowed them to walk over 
culture media. No typhoid colonies were found but only a 
few of B. coli. Similar experiments were made with B. 
prodigiosus with negative results, though the germs were 
recovered from the feet of the flies after 12 hours. 2 

Dysentery. — Auche 3 allowed flies to become contami- 
nated with cultures of the dysentery bacillus, and found that 
they could carry the germs for hours, and that the flies would 
take up the bacilli from feces as well as from cultures. 

Tuberculosis. — Spillmann and Haushalter found tubercle 
bacilli in the intestines and in the dejecta of flies that had 
fed on tuberculous sputum. Hoffmann found tubercle bacilli 
in four of six flies captured in a room occupied by a tuber- 
culous patient, and also in the excreta of flies scraped from 
the walls and furniture of the room. Lord 4 found virulent 
bacilli in flyspecks, but could not induce the disease by caus- 
ing guinea pigs to breathe air drawn over infected specks. 
Hayward 5 demonstrated living bacilli in flyspecks after the 
flies had been fed on sputum in such a way as to preclude 
the possibility of the infection of their feet or bodies. Andre 8 
demonstrated tubercle bacilli in the excreta of flies by inocu- 
lation tests, and he found that they appeared in the feces 
about six hours after feeding and continued for five days. 
Flies may also become infected by eating tuberculous dust. 

Numerous experiments have been made with various sapro- 
phytic bacteria to prove that they may be readily carried by 
insects. A common show experiment of the laboratory or 
of " health exhibitions " is to allow some insect, as a fly or 

1 Hewitt, Quart. J. Micr. 8c., 1909, n. s., LIV, 394. 

2 Ibid., 403. 

3 Auche, Compt. rend., Soc. de bid., Par., 1906, LXI, 450. 

4 Lord, Boston M. & S. J., 1904, CLI, 651. 

6 Hayward, N. York M. J. [etc.], 1904, LXXX, 643. 

6 Andre, 6th Internat. Cong, on Tuberc, Wash., 1908, I, 162. 



354 THE SOURCES AND MODES OF INFECTION 

cockroach, to walk across an agar plate leaving rows of bac- 
terial colonies to mark its footprints. In 1899 the writer, 
with the assistance of Prof. F. P. Gorham, exposed agar 
plates and dishes of milk in the pantry of a house, and poured 
large amounts of a culture of B. prodigiosus into the near-by 
privy vault. Of nine tests, four showed infection with pro- 
digiosus, while all of five plates exposed near the vault were 
so infected. Plates covered with wire netting were not 
infected. Flies were very numerous and were constantly 
walking over the plates. 

Wild Flies carry Fecal Bacteria. — Flies caught in the 
open have been shown to be at times loaded with fecal bac- 
teria, thus indicating at once their habits and the possibility 
of their carrying certain diseases. Jackson 1 found as many 
as 100,000 fecal bacteria on a single fly, and as a general 
thing the nearer the flies were to the sewer outlets the more 
numerous were this class of bacteria. Graham-Smith 2 found 
fecal bacteria on 23.6 per cent of 148 flies examined in Cam- 
bridge, England. For a part of them the surface of the body 
only was examined, and for a part the intestine only. Sur- 
face infection was about two and a half times as frequent as 
intestinal infection. The highest degree of infection was 
found among flies caught near decaying animal matter, and 
next among those caught near manure. Nash 3 recovered 
B. coli from a fly caught in a hospital ward. Delepine 4 
found bacilli of the colon type in four of thirty-five collections 
of flies caught in Manchester. 

Flies in Spanish War. — That flies are capable of carrying 
bacteria from privy vaults to food indoors, is indicated by 
the observations of Gorham noted above. Vaughan 5 also 

1 Jackson, Rep. to Com. on Pollution [etc.], of the Merchants' Ass. of 
N. York, 1907, 16. 

2 Graham-Smith, Further Preliminary Rep. on Flies [etc.], Rep. to 
Loc. Gov. Bd. on Health, n. s., 1909, 16. 

s Nash, J. Hyg., Cambridge, 1909, IX, 141. 

4 Delepine, Rep. on Health of Manchester, 1906, 85. 

6 Vaughan, J. Am. M. Ass., 1900, XXXIV, 1456. 



INFECTION BY INSECTS 355 

reports that during the Spanish War flies covered with a 
white coating of lime were often seen crawling over the food, 
the lime showing that they had just come from the latrines 
where lime had been thrown over the fecal matter. 

Species of Flies. — Flies more often than any other insect 
have been accused of thus carrying disease germs. Of these 
by far the most common in dwellings is the house fly, Musca 
domestica, though other flies are not infrequently found. In 
New York Jackson found that 98 per cent of all flies captured 
were M. domestica. In London in 1908 Austen 1 found that 
next to the house fly the most common species were Homa- 
lomyia canicularis, Calliphora erythrocephala and Muscina 
stabulans. In Providence in 1909 Sykes 2 found all the above, 
and also considerable numbers of Lucilia ccesar, Sarcophaga 

* ? and Stomoxys calcitrans, and a few Scenopinus Jen- 

estralis, but 99 per cent of the flies caught indoors were 
M. domestica. The bluebottle fly, Lucilia coesar, has been 
accused by Dutton 3 of transmitting typhoid fever. Maus 
in the Philippines blames bluebottles for the spread of 
cholera. 

Mayer 4 states that some ants were seen to pass between 
cages containing mice, some of which were sick with mouse 
typhoid and some well. The well mice soon developed the 
disease, and agar plates so placed that the ants ran over 
them showed numerous colonies of the B. murium typhi. 

Cockroaches and Other Insects. — Engelmann 5 reports 
cockroaches extremely numerous in certain houses in Chicago 
where typhoid fever prevailed, and she attributed the spread 
of the disease to these insects. Weber 6 accuses various species 
of Psocidoe of carrying tubercle bacilli from cow to cow, and 

1 Austen, Rep. to Local Gov. Bd. on Pub. Health, n. s., 1909, No. 5. 

2 Sykes, Rep. Supt. of Health, Providence, 1909, 13. 

» Dutton, J. Am. M. Ass., Chicago, 1909, LIII, 1561. 
4 Mayer, Munchen med. Wchnschr., 1905, LII, 226. 
" Engelmann, Med. News, N. Y., 1903, LXXXII, 225. 
• Weber, N. York M. J. [etc.], 1906, LXXXIV, 884. 



356 THE SOURCES AND MODES OF INFECTION 

states that he demonstrated the germs in one of these insects 
found in a manger. In fact any " domestic " insect with 
power of active locomotion, and of filthy habits, may be con- 
sidered as a possible carrier of disease germs. But the house 
fly is undoubtedly the most numerous and ubiquitous and 
the most " domestic" in its habits, and it is rightly suspected 
of playing a larger part as the mere passive carrier of disease 
germs than is any other insect. 

Flies seen to carry Infective Material. — A large number 
of observers, noting the passage of flies from infected matter 
to human beings or to food, have become convinced that 
these insects are important carriers of disease. According to 
Nuttall, Budd as long ago as 1862 considered it proved that 
-Egyptian ophthalmia is carried from child to child by the 
flies that can be observed in great numbers crawling over the ' 
face and eyes. Laveran noted the same conditions in Biskra, 
and he and many others believe that oriental sore is spread 
in the same way. Nuttall also cites several of the earlier 
writers as believing that anthrax, cholera and plague are 
transmitted by flies. After the development of bacteriology 
and the observations and experiments referred to above as 
to the power of flies and similar insects to transport bacteria, 
considerable weight was added to the arguments of those who 
saw in this mode of transmission an important factor in the 
distribution of the infectious diseases. 

Tuberculosis. 

Due to Flies. — Cobb l watched flies passing from tuber- 
culous sputum to food, and he attributes to these insects a 
large proportion of tuberculosis in man. Many health officials 
and anti-tuberculosis leagues have issued lurid bulletins illus- 
trating the agency of flies in transmitting the germs of " the 
great white plague." While it is certainly possible for the 
disease to be transmitted in this way, there is absolutely no 

1 Cobb, Am. Med., Phila., 1905, IX, 475. 



INFECTION BY INSECTS 357 

evidence that it is a factor of appreciable importance. The 
opportunities for infection with tubercle bacilli in other ways 
are so much greater and more numerous that we are not 
justified in considering infection by flies of much importance. 

Cholera. 

Due to Flies. — Cholera has of late been considered to be 
to a considerable extent a fly-borne disease. This has been 
the view of Chantemesse and Borel, 1 as well as of many of our 
officials in the Philippines, 2 as Heiser, 3 Woodruff 4 and Mc- 
Laughlin, 5 though all of the latter seem to consider contact 
infection a good deal more important than infection by means 
of flies. Nuttall cites Flugge, Macrae, Buchanan, and Tsu- 
zuki as considering flies of great importance in this disease. 

Dysentery. 

Due to Flies. — In a recent outbreak of dysentery in a 
Massachusetts asylum involving 156 cases, and carefully 
studied by Ryder, 6 flies were believed to be the chief factor 
in the extension of the disease. 

Diarrhea. 

Due to Flies. — Many of the English have been inclined 
to attribute considerable influence to the fly as a factor in the 
causation of the summer diarrheas of infants. Newsholme, 
who believes that diarrhea is due chiefly to infection of the 
milk in the house, says that opened cans of condensed milk 
are often seen to be black with flies, attracted by the sugar 
in the milk, and attributes to them no inconsiderable share in 
the causation of the disease. Sandilands, 7 like Newsholme, 

1 Chantemesse and Borel, Bull. Acad. de. m6d., Par., 1905, 3 s., LIV, 
252. 

2 Maus, Abst, Med. News, N. Y., 1902, LXXXI, 318. 

1 Heiser, J. Am. M. Ass., Chicago, 1907, XLVIII, 856. 
* Woodruff, J. Am. M. Ass., Chicago, 1905, XLV, 1160. 

6 McLaughlin, J. Am. M. Ass., Chicago, 1909, LII, 1153. 
« Ryder, Boston M. & S. J., 1909, CLXI, 681. 

7 Sandilands, J. Hyg., Cambridge, 1906, VI, 77. 



358 THE SOURCES AND MODES OF INFECTION 

finds diarrhea especially prevalent among the users of con- 
densed milk, and he thinks that the milk is probably infected 
by flies after the can is opened. Nut tall cites Copeman as 
seeing in flies the possible cause of an outbreak of diarrhea 
investigated by him. Nash l in 1903 stated his belief that 
the house fly played the chief part in the epidemiology of 
summer diarrhea. 

Typhoid Fever. 

Flies in Spanish War. — More attention has, however, been 
bestowed on the relation of the fly to typhoid fever than to 
any other disease. Sedgwick 2 was the first that I know of 
to call attention to the importance of flies as a means of 
spreading typhoid fever, but the excessive typhoid death rate 
in the home camps of our soldiers during the Spanish-Ameri- 
can War did more than anything else to call attention to the 
possible importance of the fly as a distributer of the germs of 
this disease. Surgeon General Sternberg had issued orders to 
guard against flies, but they had little effect. Veeder 3 clearly 
set forth the possibility of the transfer of fecal matter to 
food by means of flies, and he declared that flies were the 
principal cause of the prevalence of the disease in the camps. 
The report of the commission to investigate the cause of the 
fever, although laying chief stress on contact infection, for- 
cibly emphasized the part played by flies in the spread 
of the disease. 4 Vaughan, a member of the commission, per- 
sonally urged the importance of flies in the spread of this 
disease. 5 Ever since, great popular and scientific attention 
has been bestowed upon the fly in the United States and also 
in other countries. 

1 Nash, J. San. Inst., Lond., 1903, XXVI, 495. 

2 Sedgwick, Rep. Bd. Health [etc.], Mass., 1892, 736. 

3 Veeder, Med. Rec, N. Y., 1898, LIV, 429. 

* Abst. of Rep. on the Origin and Spread of Typhoid Fever in U. S. 
Military Camps during the Spanish War, 1898, 183. 

^Vaughan, J. Am. M. Ass., Chicago, 1900, XXXIV, 1451, 1496. 



INFECTION BY INSECTS 359 

Other Reports of Typhoid Fever Due to Flies. — Nuttall 
cites Quill, Tooth and Calverly, Smith, Austen, Straton and 
Jones as attributing much of the army typhoid in South 
Africa and India to the presence of flies. Numerous writers 
on typhoid fever in civil life have referred to the fly as a 
most active agent in the transmission of this disease. In 
" The House Fly at the Bar," published by the Merchants' 
Association of New York in 1909, are printed opinions of 
seventy or more health officials and others, all but nine or 
ten of whom are emphatic in their statements that flies are 
very important carriers of disease germs. Some few, how- 
ever, consider that the case against the fly has not been 
proved, though some circumstances are suspicious. Several 
give instances of fly infection that have come to their notice. 
Hurty writes of an outbreak in an asylum following the brief 
use of the privy by a walking case of typhoid fever. Flies 
abounded and there was no chance for contact. Taylor, of 
Denver, reported typhoid fever at a dairy. The milk became 
infected, he thinks by flies, for the privy was near the milk 
house, and gelatine cultures exposed near the privy and in the 
milk house showed colonies of typhoid bacilli, presumably 
deposited by flies ! Dr. H. W. Hill, the exceedingly cautious 
epidemiologist of the Minnesota State Board of Health, writes 
me that from his observations in that state he " firmly 
believes that flies are an important factor in the spread of 
typhoid in such places as mining and lumber camps, and that 
the small country village with its exposed outdoor closets 
parallels the camp conditions exactly." He further states 
that Wald noted that in a certain camp the Italians did not 
contract the disease because, as he thought, they did not eat 
between meals, while the Finns suffered severely because 
they kept their food laid out on the table all the time, where 
it was exposed to innumerable flies, and helped themselves 
during the day at random. Numerous bulletins and circulars 
have been issued by state and municipal health officials, some 
of which depict, in exaggerated language and with extrava-j 



360 THE SOURCES AND MODES OF INFECTION 

gant illustration, the danger to be feared from this household 
pest, and a distinguished entomologist has urged that the 
familiar name of M. domestica be changed from house fly- 
to typhoid fly. 

The Fly a Nuisance. — While the fly is a nuisance and 
it is highly desirable to get rid of it, and while it seems likely 
that it is to some extent a means of spreading disease, it is 
extremely unwise to make definite statements that it is the 
chief source of diarrhea, of cholera or of typhoid fever, unless 
we have very exact proof, and it is unwise, unless such proof 
is at hand, to urge large expenditures to get rid of flies, 
promising thereby the eradication of typhoid fever and other 
diseases. If it should chance that a mistake has been made, 
and that the fly is not the chief disseminator of typhoid fever, 
and the disease still persists after the fly has disappeared, 
we need not be surprised if the public fail to take us seriously 
when we advise, on knowledge that is well established, that 
mosquitoes are the sole carriers of malaria and yellow fever; 
that escape from the tsetse fly means escape from sleeping 
sickness ; and that a rat-proof city will be a plague-proof city. 

Flies suspected from their Habits. — The chief reasons 
why the fly is believed to be the carrier of diarrhea, cholera 
and typhoid fever are that flies are seen to pass from feces 
to food; that they have been shown to carry fecal bacteria, 
and in several instances the specific bacteria of cholera and 
typhoid fever ; and that they often swarm in unusual numbers 
at times and in places where there is an exceptional preva- 
lence of disease. The very definite observations of Hamilton, 
Fricker, Klein, Simmonds, Mann and Tsuzuki as to the find- 
ing of infected flies in infected houses, and the accounts given 
by Veeder, Vaughan, Tooth, Smith, Hill and others, of the 
contamination of food by flies in camps, military and civil, 
certainly render it probable that these insects do at times 
cause sickness, and may under certain conditions such as 
prevail in camps be an important factor in outbreaks. But 
these observations are far from a demonstration of what is 



INFECTION BY INSECTS 361 

now generally claimed, that flies are the chief factor in the 
spread of typhoid fever, and perhaps of summer diarrhea, in 
well-ordered civil communities. 

Diarrhea. Statistical Evidence of Fly Infection. — At- 
tempts have been made to prove by the statistical method 
the relation of flies to disease. Observations made in 
widely different localities have shown a very close relation 
between the seasonal distribution of flies and summer diarrhea. 
Stations are established at various places in a town and flies 
are caught in traps or by means of fly paper, and the number 
of flies is compared with the number of deaths from diarrhea. 
Niven 1 in Manchester, in 1903, found that the " fly curve" 
and the curve for diarrheal deaths corresponded very closely, 
and the same agreement was noted in 1905 and 1906. 2 The 
table given shows both the date of inception and the date of 
death of the fatal cases of diarrhea. In both years the max- 
imum number of cases occurred at almost exactly the same 
time as the maximum number of flies, and the maximum num- 
ber of deaths about a week later. In 1905 the maximum was 
about August 1, and in 1906 about September 5. Jackson in 
New York 3 showed a similar close relation between flies and 
diarrhea, as has Ainsworth 4 for Poona in India. Nash, 5 
showing the seasonal distribution of flies, states that in 1902, 
at Southend, there were few flies and little diarrhea in 
August, and that diarrhea increased in September as the flies 
increased. Both 1902 and 1903 had cool summers with few 
flies and little diarrhea, while 1904 and 1906 had plenty of 
flies and plenty of diarrhea. In 1904 there was a heavy local 
incidence near a large dump where flies abounded. Hamer 6 

1 Niven, Rep. on Health of Manchester, 1903, 123. 

2 Rep. on Health of Manchester, 1906, 82. 

3 Jackson, Rep. to Com. on Pollution [etc.], of the Merchants' Ass. 
of N. Y., 1907, 17. 

4 Ainsworth, J. Roy. Army Med. Corps, Lond., 1909, XII, 485. 
6 Nash, J. Hyg., Cambridge, 1909, IX, 141. 

« Hamer, Rep. Med. Off. Health, Co. of Lond., 1907, Append. II. 



362 THE SOURCES AND MODES OF INFECTION 

made a careful study of the seasonal distribution of flies in 
London, and he shows that while there is an apparent agree- 
ment between the fly curve and that of diarrheal deaths, the 
latter begins to fall before the former, which it could scarcely 
do if flies were the chief cause of the disease. Hamer is of 
the opinion that both phenomena are dependent on tempera- 
ture. In Providence, in 1909, Sykes l has shown that the 
maximum number of deaths from diarrheal diseases occurred 
about two weeks earlier than the maximum fly catch. Jack- 
son in his report has a map on which are located all the deaths 
from intestinal disease. This map shows that the great bulk 
of these are at no great distance from the water front, where 
the flies swarmed about the sewer outlets. It is just there 
that the tenements crowded with poor children are situated, 
and to maintain his argument it would be necessary to show 
an excess over and above the excess of diarrhea always found 
in tenements, and to eliminate the other unfavorable factors 
associated with poverty. 

Evidence not Conclusive. — Although there is consider- 
able evidence of a close parallelism between the seasonal dis- 
tribution of flies and of diarrhea, this parallelism is no proof 
that the latter is dependent upon the former. Even as cor- 
roborative evidence it has little value. The return of the 
sun from the equator results in a great variety of phenomena, 
many of which, though closely related in time, have no causa- 
tive relation one with another. The presence of flies seems 
to be closely correlated with the temperature, though it may 
be that the connection is far from direct. So also are a vast 
number of other events correlated with the temperature, 
though they have no causative connection with flies. A few 
years ago it was discovered that summer diarrhea developed 
only when the temperature of the soil had reached a certain 
point, and this was by many considered a demonstration 
that the germs of the disease developed in the soil. Now it 
is the fashion to say that diarrhea is due to flies because at 
1 Sykes, Rep. Supt. Health, Providence, 1909, 15. 



INFECTION BY INSECTS 363 

times the increase in flies precedes by a little the increase in 
diarrhea. While it may be that flies have much to do with 
the causation of infantile summer diarrhea, as yet we have 
no proof of it. 

Flies and Typhoid Fever. Statistical Evidence. — As the 
seasonal distribution of flies has been studied with reference 
to diarrhea, so has it been studied with reference to typhoid 
fever. Jackson, in his report to the Merchants' Association 
in New York before referred to, gives a chart showing the 
seasonal distribution of flies in New York and of deaths 
from typhoid fever, the latter being set back two months to 
allow for the assumed time between the date of infection and 
the date of death. The apex of the typhoid curve corre- 
sponds fairly well with the apex of the fly curve, but there is 
a rise in the typhoid curve in February, two-thirds as high as 
that of August, which certainly cannot be attributed to flies. 
Ainsworth in India 1 states that at Poona the maximum 
admissions of typhoid fever to the hospital occur about one 
month after the maximum fly catch. Judging from Ains- 
worth's paper, there appears to be great seasonal variation 
in the number of flies in Poona, correlated closely with the 
temperature, as with us. 

Statistical Evidence against Theory. — Niven 2 found that 
while in Manchester in 1903 the maximum number of flies 
was caught about August 29, the maximum number of 
cases of typhoid was not reached until November, during the 
whole of which month the morbidity remained high. In 
1906 3 there was as usual a well-marked maximum of flies 
about September 1, and while the typhoid morbidity was 
high in September, being 65, it was somewhat higher in Oc- 
tober, and there were 46 cases in November and 50 in January 
and only 21 in July and 23 in August. In Washington, 4 

1 Ainsworth, J. Roy. Army Med. Corps, Lond., 1909, XII, 485. 

2 Niven, Rep. on Health of Manchester, 1903, 123. 

3 Rep. on Health of Manchester, 1906, 63, 84. 

4 U. S. Pub. Health & Mar. Hos. Serv., Hyg. Lab. Bull., No. 52, 30. 



364 THE SOURCES AND MODES OF INFECTION 

in 1908, the maximum fly catch was for the week ending 
June 24, after which it steadily and rapidly decreased. 
The maximum of typhoid cases, according to date of at- 
tack, was in the week ending July 22, but instead of falling 
rapidly, as did the fly catch, it continued high until the 
middle of September. There certainly is little parallelism 
between the two curves. The commissioners appointed to 
study the disease, and who make the report, say that the 
evidence is quite strong that flies play a relatively small part 
in the spread of typhoid fever in Washington. 

In Providence the seasonal distribution of typhoid fever 
cases, according to date of first symptoms, for the six years 
1904-1909, was as follows. All cases due to milk and all 
certainly contracted out of the city are excluded. 



Jan. 
45 


Feb. 
36 


Mar. 
26 


Apr. 

48 


May 
49 


June 
56 


July 

80 


Aug. 
161 


Sept. 
133 


Oct. 
117 


Nov. 
96 


Dec. 
59 



According to observations of Sykes, the maximum fly catch 
out of doors was about the last of July, when it began to fall 
off quite rapidly. The observations as to the indoor catch 
were not very numerous, but it seems probable that the flies 
go indoors in greater numbers as the weather grows cooler in 
September. There is certainly not a very close agreement 
between the number of flies and the prevalence of typhoid 
fever. It is scarcely possible that the typhoid fever develop- 
ing in November is due to flies, and yet there were 96 cases 
in November, and the November rate is higher than that 
of any other month except August, September and October. 
If we cannot attribute the excess in November to flies, why 
should it be thought necessary to attribute the excess of 
the preceding three months to flies? I can see nothing in 
the seasonal distribution of typhoid fever in Providence to 



INFECTION BY INSECTS 365 

warrant the assumption that flies are an important factor in 
its causation. 

Local Variation in Fly Distribution. — One of the most 
interesting of Sykes' observations was the enormous variation 
in the local distribution of flies. In some of the dirtiest 
sections of the city the fly catch was 25 or 30 times as great 
as in the clean parts, and the difference in the indoor catch 
was still greater. While there is somewhat more typhoid 
fever in the fly-infested districts, the difference is not very 
marked, and a considerable excess there might be expected 
as a result of contact infection due to the uncleanly habits 
of the poorer people. There is therefore nothing in the 
local distribution of flies in Providence to warrant a belief 
that they have much to do with the spread of typhoid 
fever. 

Correlation of Typhoid Fever and High Temperature. — 
I have been able to find only the very few observations noted 
above as to the correlation of fly distribution and typhoid 
fever, and these few do not indicate that there is any reason 
to assume that the flies stand in causative relation to the 
fever. The very careful work of Sedgwick and Winslow 1 
shows that throughout the world, and in both hemispheres, 
there is a distinct relation between this disease and the sea- 
sonal rise in temperature. These authors, though they recog- 
nized a certain amount of infection by flies, explained the 
autumnal increase in typhoid fever as due to the direct and 
favorable action of high temperature on the life of the bacillus 
outside the body. This view hardly seems tenable from what 
has since been learned of the life habits of the bacillus, and I 
think is now no longer held by the authors. It is the custom 
now for most writers to attribute to flies the chief role in the 
autumnal excess of typhoid fever, but from the evidence at 
hand it seems wiser, while admitting the fact of seasonal dis- 
tribution, as determined by Sedgwick and Winslow, to await 

1 Sedgwick and Winslow, Mem. Am. Acad. Arts. & Sc, 1902, 
XII, No. 5. 



THE SOURCES AND MODES OF INFECTION 

further study before attributing this definitely to any one 
cause or group of causes. 

Control of Flies. — Nevertheless flies are a great nuisance 
and a possible source of danger, and it is very desirable that 
they should be eliminated as far as possible. Each indi- 
vidual family can very effectually control these pests by 
good screening and the use of fly paper. It is desirable that 
people should be educated to dislike flies. Chantemesse says 
that the housewife should think it as much of a discredit to 
have flies in her house as bugs in her bed. Circulars of 
information may be distributed, but care should be taken to 
avoid exaggeration, and not to promise too much either as 
to the effectiveness of remedies or the resulting decrease in 
disease. We know even now far too little about the habits 
of flies and the best ways of attacking them. Packard and 
Howard gave us our first definite knowledge, but this has 
been much extended by Newstead, 1 who showed that the fly 
is far less exclusive in its choice of breeding places than was 
supposed. Austen, Jackson, Sykes, Jepson and Hamer have 
also added to our knowledge. It appears that effective scav- 
enging is the most important means of getting rid of flies. 
If yards, streets and vacant lots were kept clean, market refuse 
removed promptly, and all garbage kept covered, there would 
be an enormous reduction in the number of flies about dwell- 
ings. The most practicable way to prevent the breeding of 
flies in stable manure is to compel its removal once a week. 
Wherever it is possible the privy vault should be abolished. 
When this is impossible, the fly-proof privy has been urged. 
To the writer this scarcely seems feasible, but Levy in Rich- 
mond is making a strong fight for it, and his efforts will be 
watched with interest. The question of covering food in 
markets and shops to protect it from flies as well as from 
dust has been much discussed. Slack 2 in an excellent paper 

1 Newstead, Rep. on the Habits, etc., of the House Fly, to the Health 
Committee, Liverpool, 1907. 

2 Slack, Am. J. Pub. Hyg., 1909, V, 159. 






INFECTION BY INSECTS 367 

concludes that the danger from this source in a well-ordered 
city is not very great, but that for aesthetic reasons the public 
might well demand, through ordinances or otherwise, that 
food be so protected. In this opinion the writer heartily 
concurs. 

Summary. — After this brief examination of the evidence 
in regard to the role of insects in the transmission of disease 
we are justified in the following conclusions: 

First. It is certain that yellow fever and malaria are trans- 
mitted solely by certain mosquitoes, and that by controlling 
the mosquitoes it is possible even under very unfavorable 
conditions, to eradicate or reduce to a minimum these two 
diseases. 

Second. It is highly probable that the relapsing fevers are 
transmitted solely by certain ticks, sleeping sickness by the 
tsetse fly, and filariasis by the mosquito. 

Third. Bubonic plague in human beings is usually trans- 
mitted from rat to man by the flea. 

Fourth. It is probable that under certain conditions, as 
in military and civil camps, and in filthy communities without 
sewerage, insects, especially flies, may be an important factor 
in the spread of the fecal-borne diseases, but there is no evi- 
dence that in the average city the house fly is a factor of 
great moment in the dissemination of disease. 



INDEX 



Page 

Actinomycosis 306 

African cattle fever 84 

Air, see Sewer air. 

bacillus influenzae not carried by 71-72 

bacillus tuberculosis in 248-249 

bacteria found in 248-251 

danger of infection by 250 

expired, free from germs 237 

infection by, thought important 95 

infection of wounds by 250-251 

pneumococcus in 250 

pus-forming bacteria in 249-250 

swine plague bacilli in 250 

Air infection, conclusions 263-265 

experiments with anthrax 262 

Mediterranean fever 261-262 

plague 262-263 

Air-borne anthrax 235-236 

influenza is not 231-232 

malaria is not 324 

measles 232 

chicken pox 224 

disease, slight evidence of 236 

infection indoors 232 

infection in surgery 233-234 

infection, reasons for belief in 213-214, 233 

scarlet fever 224-227 

out of doors 226-227 

smallpox, cases traced to other sources 222-223 

conclusions 223-224 

evidence against 220-223 

evidence of, in United States 218-219 

from hospitals 214-224 

infection of, denied 2UT-224 

objections to theory 219-220 

tuberculosis.. . 152, 160-161 

Ameba?, intestinal parasites 83 

species of 20 

Amebse dysenteric carriers, percentage of 88-89 

grown on culture media 20 

in soil 20 

in well persons 87-88 

on vegetables 20 

Amebic dysentery 20 

369 



370 INDEX 

Page 

American hospitals 100-103 

Anchylostoma, see Uncinaria, Hookworms. 

Anchylostoma duodenalis 144 

Anchylostomiasis, due chiefly to contact 144-145 

Animals, diseases of, affecting man 311-313 

Animals spread tuberculosis by licking one another 162 

Anopheles mosquitoes carry malaria 322-323 

mosquitoes, species and habits 325-326 

Anthracosis 256-257 

Anthrax, a dust-born disease 235-236 

an air-borne disease 235-236 

experiments in infection by air 262 

perpetuated by direct contact 2 

soil in relation to 2 

spread by unrecognized or concealed cases 2 

Anthrax and fomites : 184-185 

insects 349-350, 356 

due to food infection 2, 305 

bacillus, see Bacillus anthracis. 

from hair, hides 185 

morocco factories 3 

wool 185 

wool refuse * 3 

spores in dust, hair, hides, wool 184-185 

Antisepsie medicale in French hospitals 156 

Antitoxin may favor spread of disease 326-327 

Ants carry Bacillus murium typhi 355 

plague bacilli. 351 

Aspergillus destroys mosquitoes 330 

Asylums, bacillary dysentery in 141-142 

percentage of bacillus diphtheriae carriers in 62 

typhoid fever in 37 

Atoxyl to prevent sleeping sickness 342 

Babies' Hospital, gonorrhea in 123-124 

Bacillary dysentery caused by contact 43, 141-142 

culture of bacillus in eye 141-142 

in camps . 141 

in institutions 141-142 

dysentery, mild cases of 43 

Bacillus anthracis, see Anthrax spores. 

Bacillus anthracis, growth in ponds 3 

relation to the soil 2, 4 

saprophytic existence of - 

Bacillus coli communis cause of diarrhea 307 

in dust of schoolrooms 244 

on the hands 137 

Bacillus diphtheriae, carriers in family 61-62 

in insane asylum 62 

in schools 62-66 

of 54-71 

carriers, investigation of, in Massachusetts . 55 
in carriers, varieties of 55 



INDEX 371 

Page 

Bacillus diphtherial in carriers, virulence of 54, 56-58,63-64 

found intermittently 70 

in bread 22 

clay 191 

convalescents 54, 56-57, 70-71 

dust 240,244 

holy water, on cups, pencils, drinking glass 150 

membrane 198 

milk 21, 22 

otitis 66-67 

pupils cause disease in teacher 70 

rhinitis 66-67 

rooms 191, 199 

scarlet fever 58-60, 63, 68 

school children 54-58, 60, 62-66 

soil 22 

sore throats 65-66, 70-71 

well persons 54-55 

may be air-borne 239 

not in normal throats 56-57 

on coat 185 

drinking glass 150 

fomites 150-151, 185, 198-199 

fomites, virulence of 198 

pencils 151, 191 

resistance to drying 191, 240 

saprophytic existence of 21 

Bacillus dysenteriae, cause of diarrhea 307 

in convalescents 43 

feces 20 

milk 11 

soil 19 

well persons 43 

resistance to drying 192 

saprophytic existence of 19 

Bacillus enteritidis, cause of diarrhea 307 

in food poisoning 311 

Bacillus enteritidis sporogenes, cause of diarrhea 307 

Bacillus influenzae in droplets 248 

not carried by air 71-72 

widely distributed 72-73 

Bacillus influenza?, not saprophytic 22 

persistence of 72 

resistance to drying 196 

Bacillus leprae in droplets 247 

Bacillus morbificans, in food poisoning 311 

Bacillus paratyphi, cause of diarrhea 307 

Bacillus paratyphi in feces 12 

in food poisoning 311 

not found in healthy persons 39 

Bacillus pestis carried by ants 351 

in bodies of fleas 194 

convalescent guinea pigs 42 



372 INDEX 

Page 

Bacillus pestis in convalescents 42 

cow dung 19 

dust 240-241 

sputum 42 

not found on floors 193 

on cotton goods 186 

Bacillus pestis, infection of soil by 18 

resistance to drying 193-194, 240-241 

saprophytic existence of 18 

Bacillus prodigiosus on flies 354 

in droplets 245-247 

in sewer air 234 

Bacillus tetani in blank cartridges 6, 184 

dirt of floors 197 

gelatine , 6, 184 

intestines of animals : 5 

soil 6, 197 

on lamp wick 6, 184 

Bacillus tetani, latency of 78 

resistance of 6, 183-184 

saprophytic existence of 6 

Bacillus tuberculosis, carriers of 75-77 

latency of 76-77 

not saprophytic 22 

so resistant as believed 192-193 

proportion of human and bovine types . . 300-301 

resistance to drying 192-193, 199-200, 241 

Bacillus tuberculosis in air 248-249 

butter 304-305 

communion cups 153 

droplets 245-246 

dust 242-243 

flies, and fly specks 353-354 

lymphatic glands 161 

milk 295-296 

nose and mouth 75-76 151, 161 

railway carriages 242 

room 193, 242 

tonsils 161-162 

tramcars 242 

may be dust-borne 239-240 

pass from stomach to lungs 255-258 

not found in street dust 242 

in expired air 237 

on spirometer 153 

on a glass 153 

dishes 153 

fomites 152-153, 199-200, 242, 243 

hands 151-152 

napkin rings 153 

sidewalks 152 

telephones 153 

tongue 161 



INDEX 373 

Page 

Bacillus tuberculosis perishes in light 192-193 

swept from sidewalks by dresses 152 

Bacillus typhi, carriers of, never sick 31-37 

flies and 352-353 

intermittent excretion of 36 

moisture necessary to growth of 12 

path of entrance 30, 136 

resistance to drying 190-191, 240 

saprophytic existence of 7, 12 

Bacillus typhi carried on fingers 127-128 

in bone marrow 31 

bones 30 

bronchial mucus 30 

butter 12 

cerebro-spinal fluid 30 

dead animals 8 

dust ' 240 

feces 8, 31-32 

gall bladder 30 

ice 10, 269 

kidneys 30 

milk • 11 

ovaries 30 

oysters 10 

privy vaults 8 

seltzer water 10 

septic tank effluent 8 

sewage 8 

sewer air 234 

soft drinks 10 

soil 7 

epidemiological evidence of growth 12 

spleen 31 

the blood 30 

tidal mud 8 

urinary bladder 30 

urine 31 

water 9 

water, epidemiological evidence of growth 13 

modes of contamination 270 

recovered from 269 

increase in milk 13 

on blankets 185 

Bacteria and sewer air 234-235, 238-239 

Bacteria, effect of drying upon 189-190 

inhalation of 254-255 

Bacteria found in air 248-251 

in mouth 150 

not found in expired air 237 

not given off from moist surfaces 237-238 

of suppuration, see Pus bacteria. 

on cups 150-151 

fomites 197-200 



374 INDEX 

Page 

Bacteria on pencils 150-151 

money 181-182 

hands 150-152 

Bagging, yellow fever from 171 

Balantidium 83 

Ballast, yellow fever from 171 

Bathing, typhoid fever from 274-275 

Baths, public, encourage cleanliness 169 

Bedbugs and anthrax 350 

plague 347 

relapsing fever 344-345 

typhoid fever 351 

kala-azar 342 

Bed clothing, bacillus diphtherias on 198 

Bedpan carries dysentery amebse 141 

Bed, smallpox from 172 

Betel nut, cholera spread by 143 

Biological carriers distinguished from mechanical carriers 346 

Black-leg 4 

Blank cartridges, bacillus tetani in 6 

Blankets, bacillus typhi on 185 

Blood, bacillus typhi in 30 

infection of, cause of typhoid fever 30 

meningococcus in 45 

yellow fever virus in 333-334 

Boer War, typhoid fever from dust in 229-230 

flies in 359-360 

Books, bacillus tuberculosis on 199 

scarlet fever from 173 

Boophilus annulatus and cattle fever 83 

Botryomycosis 306 

Bovine tuberculosis bacillus may infect man 293-294 

Bread, bacillus diphtherise in 22 

Broad Street well 266-267, 275 

Brush, bacillus diphtheriae on 198 

Bubonic plague, see Plague. 

Butter, a source of typhoid fever 292 

bacillus tuberculosis in 304-305 

bacillus typhi in 12 

Calliphora erythrocephala 355 

Camps, bacillary dysentery in 141 

filthy condition of 138 

typhoid fever in 128-129, 258-559 

Caps and gowns to prevent infection 176, 232 

Carbolic acid in well water 274 

Carriers a recent discovery 29 

and mild cases, number of : 91-93 

cause cattle fever 83-84 

cerebro-spinal meningitis 46-53 

cholera 143 

diphtheria 66-71 

glanders 71 



INDEX 375 

Page 

Carriers cause malaria 84-86 

nagana 87 

typhoid fever 36-37 

during incubation 34 

explain spread of cerebro-spinal meningitis 50-53 

less infective than the sick 113 

more dangerous than things 183 

of amebic dysentery 87-88, 141 

bacillary dysentery 43 

cattle fever 83 

cerebro-spinal meningitis 44-53 

cholera 39-40 

diphtheria, importance of 107-110 

glanders 71 

gonorrhea 74 

influenza 71 

lepra bacilli 77 

malaria 84-86 

measles 82 

Mediterranean fever 44 

nagana 87 

parat yphoid fever 39 

plague 42 

pneumococcus 73-74 

pus organisms 77-78 

scarlet fever 80 

sleeping sickness 86-87 

smallpox 82 

tetanus bacilli 78 

tubercle bacilli 75-77 

typhoid fever 30-38 

among contacts 33-34 

cannot be isolated 110 

danger from 93 

Cartridges, bacillus tetani in 184 

Celery, typhoid fever caused by 319 

Cerebro-spinal meningitis an accident of infection 53 

due to pneumococcus 53 

Cerebro-spinal meningitis, carriers of 44-53 

explain spread of 50-53 

contagiousness of 51-52 

infection by carriers 46-53 

isolation a failure in 53, 104 

path of infection 45 

prompt isolation in, a success 104 

secondary cases 51-52 

Charbon symptomatique 4 

Charts, bacillus tuberculosis on 199-200 

Chicken pox, air-borne 224 

Children not cleanly 148 

Cholera and contact 142-143 

flies. : 352, 356-357 

fomites 173 



376 INDEX 

Paige 

Cholera caused by washing soiled linen in running streams 275 

from betel nut 143 

carriers 143 

clothing 173 

handling food 143 

rags 180 

shellfish 314 

soil 25 

unrecognized cases 16 

water 275-276 

wells 275-276 

not dust-borne 239-240 

on shipboard due to infected water 276 

outbreaks in various places 16 

Cholera, infection of nurses 143 

Cholera spirillum, see Spirillum choleras. 

Christmas presents, diphtheria from 173 

Cimex lectularius, see Bedbug. 

Citellus beecheyi 346 

Clams, typhoid fever from 315 

Clay, bacillus diphtherias in 191 

Cleanliness, education in, needed 166-167 

municipality should encourage 168-169 

Cleanliness in school, teaching of 167-168 

neglected 164-166 

rare 136-138 

in children 148 

versus disinfection 211 

Cloth, yellow fever from 171 

Clothing as fomites 174 

Clothing, bacillus tuberculosis on 200 

cholera from 173 

infection by, rare 175-177 

leprosy in 174 

scarlet fever not from 175 

typhoid fever from 177 

typhus fever not from 174-175 

Coat, bacillus diphtherias on 185 

scarlet fever from 173 

Cockles, typhoid fever from 315-316 

Cockroaches and disease 355 

Colon bacillus, see Bacillus coli communis. 

Communion cups, bacillus tuberculosis in 153 

individual, adopted 168 

Conductors not infected by money 182 

Contact by drinking cups 147-148, 150 

chief mode of infection 153-164 

infection and fingers 146-147 

infection less easy in some diseases than in others .... 145-146 

most obvious 122 

in amebic dysentery 141 

bacillary dysentery 43, 141-142 

diarrhea 143 



INDEX 377 

Page 

Contact infection in diphtheria 154-160 

cerebro-spinal meningitis 45-46, 48-49, 52 

cholera 142-143 

gonorrhea 123-125 

influenza 231-232 

measles 157 

Mediterranean fever 262 

scarlet fever 154-160 

syphilis 122, 125-127 

tuberculosis 162-163 

typhoid fever 13, 127-141 

in civil life 129-131 

typhoid fever, amount of 135-136 

evidences of 135 

in hospitals 156-160 

opportunities for 137-138 

role of privies 138-140 

Spanish war 128 

why disregarded 137-139 

uncinariasis 144 

infection, disregard of 165-166 

importance of 164 

opportunities for 148-150 

Contact, indirect, vehicles for 146-148 

mode of infection between families 154-156 

with missed cases, importance of 148-150 

with well carriers, importance of 149-150 

Contacts, typhoid carriers among. . . 33-34 

diphtheria carriers among 61 

Contagiousness, factors involved 111-113 

Contagiousness less outside family : 112-113 

than believed 111-113 

of carriers less than that of sick 113 

Convalescents, diphtheria bacilli in 56, 57 

dysentery amebse in 88 

dysentery bacilli in 43 

cholera spirilla in 39-40 

malarial parasites in 84-86 

meningococci in 46-49 

plague bacilli in 42 

pneumococci in 73 

typhoid bacilli in 31, 35 

Cornet, diphtheria from 173 

Cotton goods, bacillus pestis on 186 

Cotton, smallpox from . : 172 

Cow dung, bacillus pestis in 19 

Cows, diphtheria in 290 

scarlet fever said to occur in 289-290 

Crawfish and typhoid fever 318 

Cubicles for isolation in French hospitals 156-158 

Culex, experiments with 323 

Culex fasciatus and yellow fever 332 

Culex fatigans and dengue 343 



378 INDEX 

Page 

Culex fatigans and filariasis 339 

Culicides 328-329 

Culicides, mosquito destruction by 330, 337 

Culture method of diagnosis, introduction of 95-96 

Cups, bacteria on 150-151 

Dead animals, bacillus typhi in 8 

Dead bodies, spirillum cholerae in 15 

Dengue transmitted by mosquitoes 342-343 

Dermacenter andersoni 345 

Diarrhea, bacteria which cause 307 

Diarrhea due to condensed milk 308-309 

contact 143-307 

dust 230-231 

flies 357-358 

statistical evidence 361-363 

milk 306-309 

not always 143 

water 277-278 

Diarrhea, explosive outbreaks 309 

nature of 306-307 

prevention of 309-310 

relation of feeding to 307-309 

Diphtheria, atypical 64-66, 91 

chronic 71 

extension in dwellings 155-156 

family infection 61-62 

not from soil 24 

of extra-corporal origin 25 

similarity to scarlet fever 78-79 

warning sign in 109 

with recurrent ear discharge causes infection 70 

Diphtheria bacillus, see Bacillus diphtheriae. 

carried to homes by discharged scarlet fever cases ... 70 

carriers, importance of 107-110 

isolation of, often impossible 108-110 

cultures introduced 95-96 

value of findings 56-57 

from carriers 67-71 

Christmas presents 173 

cornet. 173 

drinking glass 150 

fomites 173-185 

milk 68-69, 289-290 

pitcher 69 

sewer air 227 

teacher 69 

tools 173 

in cows 290 

Owatonna, Minn 102 

Providence 94, 96 

Willard State Hospital 102 

isolation, duration in Providence 101 



INDEX 379 

Page 

Diphtheria isolation in institutions, failure of 101-103 

isolation, principles of 107-110 

mild cases found by cultures 96 

not air-borne in hospitals 227-228 

dust-borne 240 

Disease rarely carried by physicians 175 

Dishes, bacillus tuberculosis from 153 

Disinfection desirable at times 210 

in Providence 95 

abandoned 206-208 

schools 209 

of little value 205-209 

unnecessary in certain diseases 209-210 

versus cleanliness 211 

Disinfection, English views on 208-209 

French views on 208 

objections to 210-211 

Dog drinks from the drinking glass on train 148 

Drainage, mosquito destruction by 330 

Dresses, bacillus tuberculosis on 152 

Drinking cups, contact by 147-148 

Drinking glass, bacillus diphtheria) on 150 

common, abolished 168 

Droplet infection 245-248 

Droplets, bacillus influenzae in 248 

bacillus lepra? in 247 

bacillus prodigiosus in 245-247 

bacillus tuberculosis in 245-246 

pneumococcus in 248 

streptococcus salivarius in 247 

Droplets versus dust 253-255 

Drying, effect upon bacteria 189-190, 238-239 

resistance of bacillus diphtheria? to 191-240 

bacillus pestis to 193-194 240-241 

bacillus dysenteria) to 192 

bacillus influenza^ to 196 

bacillus tuberculosis to 192-193, 199-200, 241 

bacillus typhi to 190-191 240 

gonococcus to 197 

meningococcus to 196-197 

micrococcus of Mediterranean fever to 191 

pneumococcus to 196 

protozoa to 200 

pus-forming bacteria to 194-195 

smallpox virus to 202 

spirillum cholera to 105-196, 200, 241-242 

spirochete of syphilis to 197 

-pores to 190 

vaccine virus to 200-202 

Dust, anthrax spores in L85 

bacillus coli communis in 244 

bacillus diphtheria) in 240 244 

bacillus pestis in 240-243 



380 INDEX 

Page 

Dust, bacillus tuberculosis in 242-243 

bacillus typhi in 240 

danger from slight 244-245 

micrococcus melitensis in 17, 250 

meningococcus in 239-240, 243 

pneumococcus in 243-244 

pus organisms in 244 

Dust infection 238 

versus droplets 253-255 

Dust-borne disease 238-240 

disease, anthrax 235-236 

diarrhea 230-231 

influenza 231 

Mediterranean fever. . 262 

poliomyelitis 232 

tuberculosis , 238, 241-243, 251-261 

typhoid fever 229-230 

Dwellings, extension of diphtheria in 155-156 

scarlet fever extension in 154-155 

Dysentery, see Bacillary dysentery. 

amebic 87, 141 

amebic, due to chronic carriers 141 

infection from bedpan 141 

produced in men by amebse grown in culture . 20 

monkeys by amebae 20 

transmitted by contact 141 

infection by water 276-277 

Dysentery bacillus, see Bacillus dysenteriae. 

due to flies 353, 357 

Ear discharge causes diphtheria 70 

East coast cattle fever 84 

Elephantiasis 339 

Endemic diseases 25-26 

English hospitals 97-100 

isolation in 158-160 

Entameba coli and entameba histolytica, distinction between. ... 88 
Erysipelas from rags 180 

Family, carriers in, cerebro-spinal meningitis 47 

diphtheria 61 

infection of, in house 24, 154-156 

isolation in 118-119 

typhoid fever by contact in 134 

Feces, bacillus dysenteriae in 20 

paratyphi in 12 

typhi in 8, 31, 32, 36 

typhi in, persistence of 31-32 

intermittency of 36 

hookworms in 145 

spirillum cholenc in 15 

Filaria bancrofti 338 

Filariasis and mosquitoes 338-339 



INDEX 381 

Page 

Filth theory of disease 23 

Filtration of water 282 

reduces typhoid fever 271 

Fingers and contact infection 146-147 

Fish, infection by fried 318 

Fishermen, influenza among 231 

Fleas and anthrax 350 

plague 19, 262-263, 346-349 

Fleas, bacillus pestis in 194, 347-348 

Flies a nuisance 360 

and anthrax 3, 356 

cholera 352, 356-357 

diarrhea 357-358 

diarrhea, statistical evidence 361-363 

dysentery 353, 357 

Egyptian ophthalmia 356 

plague 356 

typhoid fever, 127-129, 140-141, 358-360 

statistical evidence 363-365 

carry fecal bacteria 354 

germs 351-354, 356 

lime from privies 354-355 

Flies, bacillus tuberculosis in 353-354 

control of 366-367 

habits bring them in contact with excrement 360-361 

infected, in typhoid houses 352 

local variation in distribution 365 

species in houses 355 

tuberculosis due to 353, 356-357 

Flock cough from rags 180 

Floors, bacillus pestis not on 193 

tetani in dirt of 197 

Fly specks, bacillus tuberculosis in .• 353 

Fomites: Bagging 171 

Ballast 171 

Barbers' utensils 126 

Barracks 48, 174 

Bedding 126, 172 

Blankets 185 

Books 173, 199 

Bru^h 198 

Cartridges 6, 184 

Charts 199, 200 

Christmas presents 173 

Clay 191 

Cloth 171 

Clothing 127, 173-174, 177, 200 

Coat 173, 185 

Communion cups 153 

Cornet 173 

Cotton 172 

Cotton goods 186 

Cups 150, 151 



382 INDEX 

Page 

Fomites: Dentists' tools 126 

Drinking glass 126, 147-148, 150, 153, 198 

Floors 193, 197 

Furniture 199 

Gelatine 6, 184 

Glass blowers' tubes 126 

Grain 171 

Hair 173, 184, 185 

Handkerchief 126, 192, 198, 243 

Hides 184, 185 

House, see Room 

Lamp wick 6, 184 

Letters 173 

Linen, soiled 172, 198, 133 

Lumber 172 

Mattress 171 

Merchandise 171 

Mirror 198 

Money 126, 181, 182 

Napkin rings 158 

Nursing bottles 126 

Oyster buckets 171 

Pencils 126, 150, 151, 191 

Pins 126 

Pitcher 69 

Rags 127, 180 

Railway carriages 242 

Roller towel 168 

Room 172, 174, 177-180, 191, 193, 199, 242, 244 

Rugs 181 

Shoes 176, 198 

Spirometer 199 

Spoons, etc 126 

String 126 

Surgeons' instruments 126 

Telephones 153, 199 

Thermometer 132 

Tools 173 

Toys 198 

Tramcars 242 

Wind instruments 126 

Wool 184, 185 

Fomites and anthrax 184-185 

cholera 173 

diphtheria 173, 185 

plague, experiments in India 204-205 

observations in Sydney 203-204 

scarlet fever 172-173 

smallpox 172 

tetanus 183-184 

tuberculosis, lack of experiments 205 

typhoid fever 185 



INDEX 383 

Page 

Fomites and yellow fever 171-172, 334 

fever, experiments in Havana 203 

thought important 95 

Fomites, bacillus diphtheriae on 198-199 

bacillus tuberculosis on 199-200 

bacteria of suppuration on 21 

bacteria on 197-198 

clothing as, 174 

conclusions concerning 211-212 

definition of term 170-171 

evidence of infection by, unsatisfactory 182-183 

reasons for belief in 186-187 

Fomites infection, bacteriological evidence 188-189 

evidence against 187-188 

few instances of 186 

Food infection and cholera 143 

tuberculosis 312-313 

typhoid fever 127-128, 304, 314-319 

poisonings 311-312 

Food, handling by contacts 120-121 

spirillum cholera? in 16 

Foot-and-mouth disease and milk 306 

French hospitals 156-158 

French hospitals, "Antisepsie medicale" in 156 

cubicles for isolation in 156-158 

screens for isolation in 156-158 

Furniture, bacillus diphtheriae on 199 

Gelatine, bacillus tetani in 6, 184 

Glanders, carriers of 71 

Glands, bacteria of suppuration in 21 

cervical and mesenteric, bacillus tuberculosis in 161 

Glass, bacillus diphtheriae on 198 

tuberculosis on 153 

contact infection by drinking from 147-148 

Glossina morsitans 87 

palpalis 86, 339-341 

Goats and Mediterranean fever 17, 44, 305 

Gonococcus, not saprophytic 22 

resistance to drying 197 

Gonorrhea, air-borne infection not possible 124-125 

infection by fomites impossible 124-125 

latency of 74-75 

persistence of 74-75 

Gonorrhea believed to be spread by contact 122-127 

carried by nurses 121-125 

in Babies' Hospital 123-124 

not dust-borne 239 

Gown and cap for physicians and nurses in contagious cases 176 

Grain, yellow fever from 171 

Ground squirrels and plague 346 

Guinea pigs, bacillus pestifl in 42 



384 INDEX 

Page 

Hair, anthrax spores in 184-185 

scarlet fever from 173 

Handkerchief, bacillus diphtheria? on 198 

tuberculosis on 192, 243 

Hands, bacillus coli communis on 137 

tuberculosis on 151-152 

pus bacteria on 150-152 

Hands should be washed 137-138 

Hides, anthrax spores in 184-185 

Holy water, bacillus diphtherias in 150 

Homalomyia canicujaris 355 

Home isolation effective 118 

Hookworms, see Uncinaria, Anchylostoma 144-145 

enter through skin , 145 

grow in soil 144 

in feces , 145 

Hospital, isolation in 119 

Hospital isolation, failure of 97-100 

Hospitals, bacillary dysentery in 141-142 

contact infection in 156-160 

diphtheria not air-borne in 227-228 

scarlet fever, not air-borne from 226-227 

smallpox, air-borne infection from 214-224 

typhoid fever by contact in 131-132 

value of 118 

Hospitals in America 100-103 

England 97-100 

France 156-158 

House, infection from family to family 24 

of, cause of scarlet fever 172-173 

tuberculosis infection in 163, 178-180 

Houses, species of flies in 355 

Ice, bacillus typhi in 10, 269 

infection by 283-285 

Ice cream, a source of disease 292 

Incubation stage infective . .' 34 

Infection, former theories of 1 

Infection not so easy as believed 149-150 

Influenza, atypical cases 71 

Influenza among fishermen 231 

lighthouse keepers 231 

bacillus, see Bacillus influenzae 

from rags 180 

not air-borne 231-232 

carried across Atlantic 231 

dust-borne 231, 239 

spread only by contact 231-232 

Inhalation of bacteria 254-255 

Insect-borne disease usually due to protozoa 320-321 

Insects, first proof of transmission of disease by 321-322 

infection by, importance of subject 320 

summary 367 



INDEX 385 

Page 
Insects, Texas cattle fever first disease proved to be carried by. . 321-322 

Insects as biological and mechanical carriers 320-322 

carry germs on bodies 351 

Isolation, causes of failure 105-107 

duration of 118-120 

value of 109-110 

Isolation a failure in cerebro-spinal meningitis 104 

measles 103-104 

smallpox 105 

Isolation effective if prompt 104, 115-116 

in Michigan 114-116 

rare diseases 116-117 

hospitals, failure of 97-100 

in American cities 100-103 

English hospitals 158-160 

family 118-119 

family, effective 118 

hospital 119 

Monsall Hospital 158-160 

Providence 94, 118 

villages 113-116 

not effective in extensive outbreaks 116 

to be too strict 109-110 

of cerebro-spinal meningitis 104 

diphtheria 94, 95-97, 101, 107, 114 

diphtheria, duration in Providence 101 

malaria 328 

measles 103, 114 

plague 348 

rare diseases 114 

scarlet fever 94, 97, 114 

school children 120 

sleeping sickness 341 

smallpox 97, 105, 114 

typhoid fever 110, 114 

wage earners 110, 120-121 

yellow fever 336 

should vary 113 

too rigorous 110-111 

useless if many carriers 117 

Jews do not eat shellfish 316 

Kala-azar and insects 342 

transmitted by bedbugs 342 

Kala-azar, protozoan discovered 342 

Kissing means of spreading syphilis 126 

spread of tuberculosis 160-161 

Laboratory infection, bacillary dysentery 141-142 

typhoid fever 133 

Laboratory, tuberculosis infection in 258-259 

Lamblia 83 



386 INDEX 

Page 

Lampwick, bacillus tetani on 6, 184 

Latency of infection common 78 

Laundress contracts smallpox 172 

typhoid fever 133 

Laundries and disease 176-177 

tuberculosis 177 

Leishmania donovani 342 

Leprosy, bacilli remain latent 77 

isolation of 114 

Leprosy in clothing 174 

Letters, scarlet fever from • 173 

Lice and relapsing fever 345 

Light, bacillus tuberculosis perishes in 192-193 

Lighthouse keepers, influenza among 231 

Linen, soiled, smallpox from 172 

typhoid fever from 133, 177 

Lockjaw, see Tetanus. 

Lucilia csesar 355 

Lumber, smallpox from 172 

" Lung Blocks" in New York 178-180 

Lupus due to inoculation with saliva 161 

Malaria, an endemic disease 25-26 

anointing the skin in 329 

clearing of space about dwellings 329 

discovery of insect transmission 322-323 

experiments on infection of human beings 323 

isolation sometimes necessary 328 

killing of mosquitoes in houses 328 

latency of 84-86 

latency of, explanation 85-86 

in children 85-86 

latency, percentage, of 85-86 

mosquito sole carrier of 323-325 

screening of patients 328 

success of mosquito destruction 330-331 

ways of prevention 326-330 

Malaria and insects 322-332 

water 324 

not air-borne 324 

due to soil infection 26 

from water 278-279 

on ship Argo 278 

Malta, Mediterranean fever exterminated at 44 

Malta fever, see Mediterranean fever. 

Mattress, yellow fever from 171 

Measles an air-borne disease 232 

Measles, carriers of 82 

disinfection after 208 

isolation in, a failure 103-104 

not from soil 24 

number attacked 82 

per cent of children attacked 103 



INDEX 387 

Page 

Meat and tuberculosis 312-313 

Meat, infection by 311-314 

inspection, federal control of 313-314 

Mechanical carriers distinguished from biological carriers 346 

Mediterranean fever an endemic disease 17 

and contact infection 262 

dust 262 

goats 17, 44, 305 

caused by milk from infected goats 17, 305 

Mediterranean fever, experiments in infection by air 261-262 

exterminated at Malta 44 

goats carriers of .... - 44 

human carriers of 44 

in United States 305 

micrococcus of, resistance to drying 191 

on a steamship 44 

spread by urine 18 

Membrane, bacillus diphtheriae in 198 

Meningitis, cerebro-spinal, see Cerebro-spinal meningitis. 

Meningococcus causes rhinitis 45 

found intermittently .' 48 

only near sick 49 

in air 49 

contacts 45-46, 48-49, 52 

dust 239-240, 243 

families 47-52 

normal nose 45 

nose in sickness 44 

Meningococcus, infection in barracks 48 

not saprophytic 22 

persistence of infection 46-47 

resistance to drying 196-197 

Merchandise, yellow fever from 171 

Michigan, isolation effective in 114-116 

Micrococcus albus 20 

aureus 20 

citreus 20 

nelitensis, discovery and study of 17 

in dust 17,250 

resistance to drying 191 

saprophytic existence of 17 

meningitidis, see Memingococcus. 
pneumoniae, see Pneumococcus. 

Mild cases of infectious disease not recognized 92-93 

Milk, bacillus diphtheriae in 21-22 

dysenteriae in 11 

tuberculosis in 295-296 

typhi in 11-13 

classification of 303 

condensed and diarrhea 308-309 

diarrhea from 306-309 

diphtheria from 68-69, 289-290 

foot-and-mouth disease from 306 



388 INDEX 

Page 

Milk, handling by contacts 120-121 

increase of bacillus typhi in 13 

infection by water 273 

from human sources 290-291 

Mediterranean fever from 305 

mode of infection of 290-291 

pasteurization of 291-292 

protection against tuberculosis from 302-303 

of 291-292 

rabies from 306 

scarlet fever from 289-290 

spirillum cholerse in 15 

sterilization of vessels 291 

' tuberculous, consumed by children 297-300 

typhoid fever from 37, 286-288 

tuberculosis from, 294-302 

tuberculosis from, amount of 296-302 

epidemiological evidence 301-302 

instances of 300 

Milk and disease 285-310 

outbreaks, characteristics 285-286 

few in large cities 287-288 

frequency of 286-287 

source of infection 289-290 

Miners, typhoid fever among 140 

Minnesota, smallpox isolation abandoned in 105 

Mirror, bacillus diphtheriae on 198 

Missed cases a recent discovery 29 

Moist surfaces, bacteria not given off from 237-238 

Money and disease 181-182 

Money, bacteria on 181-182 

Monkeys, dysentery in 20 

Monsall Hospital, isolation in 158-160 

Montana, smallpox isolation abandoned in 105 

Mosquito destruction by culicides 330, 337 

drainage 330 

oiling 330 

prevention 329-33 

Mosquitoes and dengue 342-343 

filariasis 338-339 

malaria 322-323 

malaria, conditions for carrying 325, 326 

yellow fever 332-338 

yellow fever, destruction of 337 

habits 335 

Mosquitoes, destruction of, in malarious houses 328 

habits of 325 

species which carry malaria 322-323, 325 

success of measures for extermination 330-331 

transportation of 335 

Mouth, bacillus tuberculosis in 75-76, 151 

bacteria in 150 

pneumococcus in 73-74 



INDEX 389 

Page 

Mucous surfaces, bacteria of suppuration on 20 

Mud dumped near intake cause of typhoid fever 270 

Municipal versus personal prevention 166 

Murium typhi, bacilli of, carried by ants 355 

Musca domestica 355 

Muscina stabulans 355 

Mussels, infection by 315-317 

Myzomyia ludlowii 325 

Xagana 87 

North Boston well 267 

Nose, bacillus tuberculosis in 75-76, 151, 249 

meningococcus in, in sickness 44 

in normal 45 

tuberculosis of 162 

Nurses, gown and cap for, in contagious cases 176 

typhoid fever among 131-132 

Nurses infect patients with typhoid fever 132 

Oiling, mosquito destruction by 330 

Ornithodorus moubata 344 

Ophthalmia, Egyptian, carried by flies 356 

Opsonic index in typhoid carriers 35 

Otitis, bacillus diphtherise in 66-67 

Owatonna, Minn., diphtheria in 102 

Oyster buckets, yellow fever from 171 

Oysters, bacillus typhi in 10 

"fattening" of 317 

infection by 314-318 

Pail-closets cause typhoid fever 139-140 

Paratyphoid bacilli, see Bacillus paratyphi. 

Pencils, bacillus diphtheria? on 151, 191 

bacteria on 150-151 

Personal versus municipal prevention 166 

Persons, not things, are dangerous 183 

Physicians, gown and cap for, in contagious cases 176 

Physicians rarely carry disease 175 

Pigment to lungs from stomach 256 

Piroplasma bigeminum 83, 321-322 

Placards for contagious diseases 109 

Plague and bedbugs 347 

fleas 19, 262-263, 346-349 

fleas, epidemiological evidence 347-348 

experimental work 347-348 

flies 356 

fomites, experiments in India 204-205 

observations in Sydney 203-204 

ground squirrels 346 

other rodents 346-349 

rats 19, 42, 346-349 

rugs 181 

bacillus, see Bacillus pestis. 



390 INDEX 

Page 

Plague not dust-borne 239-240 

Plague, atypical human 42 

rat 41 

chronic in rats 41 

experiments in infection by air 262-263 

isolation of 348-349 

Plasmodium 84, 324-325 

Pneumococcus cause of meningitis 53 

in air 250 

convalescents 73 

droplets 248 

dust 243-244 

normal mouths 73-74 

may be air-borne 239 

not dust-borne 240 

Pneumococcus, not saprophytic 22 

persistence of 73 

resistance to drying 196 

virulence of, in carriers 73-74 

Poisoning by food 311-312 

Poliomyelitis a dust-borne disease 232 

Privies and water-closets usually filthy 137-138 

encourage uncleanliness 140, 169 

infect water supplies 270 

Privies, removal of, causes decrease of typhoid fever 139-141 

typhoid fever from 127-128, 137-141 

Privy vaults, bacillus typhi in 8 

Prosedemic infection, typhoid fever by 130 

Proteosoma in birds 323 

Protozoa, difficult to cultivate 23 

not saprophytic 22 

resistance to drying 200 

Protozoan diseases, latency in 82-83 

Psocidae and disease 355-356 

Pulex irritans 347 

Purification of water 282-283 

Pus bacteria 20 

in air 249-250 

dust 244 

glands 21 

schoolrooms 244 

skin and mucous surfaces 20 

tonsils 20 

water 21 

may be dust-borne 239-240 

on fomites 21 

Pus bacteria, distribution of 198 

resistance to drying 194-195 

saprophytic existence of 20-21 

Quarantine and sleeping sickness 341 

yellow fever 336 

officers take the temperature of passengers 89 

Quinia prevents malaria 320-328 



INDEX 391 

Page 

Rabies from milk 306 

Rags and disease 180-181 

Rags, cholera from 180 

erysipelas from 180 

flock cough from 180 

influenza from 180 

scarlet fever from 180 

septicemia from 180 

smallpox from 180-181 

typhoid fever from 180 

Railway carriages, bacillus tuberculosis in 242 

Rat-proofing of buildings 349 

Rats and plague 19, 41-42, 346-349 

Rats, carriers of plague 42 

chronic plague in 41 

destruction of 349 

Relapsing fever and bedbugs 344-345 

lice 345 

ticks 343-344 

Rhinitis, bacillus diphtheriae in 66-67 

Rhinitis caused by meningococcus 45 

Rhode Island, death rate from typhoid fever 14 

Rice, spirillum choleras in 16 

Rocky Mountain fever and ticks 345 

Rodents, plague derived from 346-349 

Roller towel should be abolished 168 

Room, bacillus diphtheriae in 191, 199 

tuberculosis in 193 

Room infection cause of typhoid fever in barracks 174 

Rooms, infection of 163, 172-173, 177-180 

Rugs and plague 181 

Saliva, bacteria in 150 

inoculation with, cause of lupus 161 

transfer of 147 

Saliva vehicle of infection 146-148 

Sarcophaga . 355 

Scarlet fever, air-borne 224-227 

air-borne, out of doors 226-227 

atypical 79-80 

atypical, frequency of 80 

extension in dwellings 154-155 

not from soil 24 

virulence varies in .• 98 

Scarlet fever and fomites 172-173 

books 173 

clothing 175 

coat 173 

house infection 172-173 

letters 173 

milk 289-290 

rags 180 

hospital temporarily closed in Leicester 99 



392 INDE X 

Page 

Scarlet fever hospitals in England 97-100 

in Providence 94 

like diphtheria 78-79 

not air-borne from hospitals 226-227 

said to occur in cows 289-290 

Scenopinus fenestralis 355 

School children, isolation of 120 

disinfection 209 

School, teaching cleanliness in • 167-168 

Schoolrooms, bacillus coli communis in 244 

pus organisms in 244 

Screening of cases of malaria 328 

yellow fever 336-337 

for protection against malaria 328 

Screens for isolation in French hospitals 156-158 

Sedgwick, typhoid fever outbreak in Bondville, Mass 127 

Seltzer water, bacillus typhi in 10 

Septic infection and insects 350-351 

tank effluent, bacillus typhi in 8 

Septicemia from rags 180 

Sewage, bacillus typhi in 8 

Sewer air and bacteria 234-235 

diphtheria 227 

typhoid fever 228-229 

Sewer air, bacillus prodigiosus in 234 

bacillus typhi in 234 

infection by. 247, 249 

Sex of smallpox cases 221 

Sheet hung before door to prevent infection 232 

Shellfish, infection by 314-318 

Shipboard, influenza on 231 

malaria on 278 

typhoid fever by contact on 134 

Ships for smallpox hospitals 216-217 

Shoes as carriers of infection 176 

Shoes, bacillus diphtheria? on 198 

Sidewalks, virulent bacilli tuberculosis on 152 

Skin, bacteria of suppuration in 20 

hookworms enter through 145 

Sleeping sickness, an endemic disease 26 

atoxyl to prevent 342 

discovery of trypanosome 339-340 

is it carried mechanically? 340-341 

modes of transmission 339-341 

not due to soil infection \ 26 

per cent of carriers 86-87 

persistence of infection 86-87 

prevention of 341-342 

quarantine 341 

Sleeping sickness and tsetse flies 339-341 

in lower animals 340 

Smallpox, air-borne, conclusions 223-224 

evidence against 220-223 



INDEX 393 

Page 

Smallpox, air-borne, objections to theory 219-220 

sex of cases 221 

air-borne infection of, denied 217-224 

in United States 218-219 

atypical cases 91 

isolation in, often a failure 105 

mild cases of 81-82 

not from soil 24 

Smallpox and fomites 172 

rags 180-181 

carriers 82 

hospital ships 216-217 

virus, resistance to drying 202 

Soft drinks, bacillus typhi in 10 

Soil, amebae dysenteriae in 20 

bacillus diphtherias in 22, 24 

dysenteriae in 19 

pestis in 18 

tetani in 197 

typhi in 7 

hookworms grow in 144 

melitensis micrococcus in 17 

not infected with cattle fever 26 

malaria 26 

measles 24 

scarlet fever 24 

sleeping sickness 26 

smallpox 24 

Texas cattle fever 26 

yellow fever 26 

spirillum cholerae in 15, 16 

Soil infection, cholera from 25 

typhoid fever from 25 

Soil infection in common diseases 24 

Spanish-American War, typhoid fever in 13, 38 

from dust in 229-230 

Spirillum cholerae found in water 276 

grow only in human body 16 

in convalescents 39-40 

cooked food 16 

dead bodies 15 

feces 15 

healthy persons 40 

milk 15 

soil 15, 16 

water 15 

Spirillum cholerae, resistance to drying 195-196, 200, 241-242 

saprophytic existence of 15 

Spirocheta carteri 345 

duttoni 344 

Spirochete of syphilis, latency of 87 

not saprophytic 22 

resistance to drying 197 



394 INDEX 

Page 

Spirometer, bacillus diphtheria? not on 199 

tuberculosis not on 153 

Spitting should be forbidden 169 

Spores may be dust-borne 240 

Spores, resistance to drying 190 

Springs as sources of infection 274 

Sputum, bacillus pestis in 42 

Squirrels, see Ground squirrels (Citellus beecheyi). 

Stamp out disease, failure to 93-94 

Steogmyia calopus 332, 335 

Sterilization of municipal water supplies 283 

Stomach, bacillus tuberculosis may pass to lungs from 255-258 

Stomoxys calcitrans 355 

Storage of water 282 

Street dust, bacilli tuberculosis not found in. . 242 

Streptococcus enteritidis, cause of diarrhea 307 

may be air-borne 239 

pyogenes 20 

salivarius in droplets 247 

Suppuration, bacteria of, in healthy organs . . .■ 77-78 

latency of bacteria of 77-78 

Suppuration result of infection by bacteria 20 

Surgery, air-borne infection in 233-234 

Swine infected by bacillus tuberculosis through the tonsils .... 161-162 

plague bacilli in air 250 

Syphilis, air-borne infection not possible 125 

articles infected with 126-127 

believed to be spread b}' contact 122-127 

droplet infection in 125 

fomites infection in, not important 127 

infection by non-sexual contact 126-127 

kissing 126 

sexual act chief mode of infection 126 

spirochete of, see Spirochete of syphilis. 

Syphilis infection not persistent 126-127 

spread solely by contact 125-126 

Tabanus lineola • 3 

Teacher caused diphtheria 69 

contracts diphtheria from pupil 70 

Telephones, bacillus diphtheria? not on 199 

tuberculosis on 153 

Tetanus and fomites 183-184 

bacillus, see Bacillus tetani. 

from lamp wick used for tying umbilical cord 5, 184 

in Red Bank, N.J 5 

on Long Island 5 

Tetanus, decrease of, in Havana 184 

Texas cattle fever, an endemic disease 26 

persistence in blood 84 

fever carried by tick 83-84 

first disease proved to be carried by insects .321-322 
not due to soil infection 26 



INDEX 395 

Page 

Thermometer transfers bacillus typhi 132 

Things not dangerous as persons 183 

Ticks and East Coast or African cattle fever 84 

relapsing fever 343-344 

Rocky Mountain fever 345 

Texas cattle fever 83-84, 321-322 

Tidal mud, bacillus typhi in 8 

Tongue, bacillus tuberculosis on 161 

Tonsils, bacillus tuberculosis in 161-162 

bacteria of suppuration in 20 

tuberculosis infection through 256 

of 162 

Tools, diphtheria from 173 

Toys, bacillus diphtheria on 198 

Tramcars, bacillus tuberculosis in 242 

Treasurer of United States, investigation of money as carrier of 

disease by 182 

Treponema pallida, life of, short ' 125 

Trier, typhoid fever in 13, 39 

Trypanosoma gambiense 86, 339-341 

brucei 87 

Tsetse flies and sleeping sickness 86, 339-341 

nagana 86 

Tuberculosis and fomites, lack of experiments 205 

laundries 177 

meat 312-313 

bacillus, see Bacillus tuberculosis. 

from flies 353, 356-357 

house infection 178-180 

milk 294-308 

milk, amount of . . 296-302 

epidemiological evidence 301-302 

instances of 300 

protection against 302-303 

water 279-280 

infection by air 152, 160-161 

in animals through mouth and pharynx. 162, 256 

laboratory 258-259 

alimentary tract 161-162 

infection, experiments under natural conditions. .259-261 

unnatural conditions of experiment 258 

of the nose 162 

tonsils 162 

spread by animals licking one another 162 

kissing 160-161 

through tonsils 162, 256 

Tuberculosis, bovine, eradication of 304 

contact infection in 162-163 

experiments concerning air-borne infection 251-261 

feeding experiments 294-295 

human and bovine reciprocally infective 292-293 

infection by dust questioned 252-253 

stomach 255-258 



396 INDEX 

Page 

Tuberculosis, infection by, in the home 163 

mode of infection, evidence from pathology 163 

proportion of human and bovine types of bacillus . 300-301 

Tuberculous milk consumed by children 297-300 

Typhoid bacillus, see Bacillus typhi. 

carrier at Bristol, Eng 37-38 

carriers 14, 30-39, 138 

among contacts 33-34 

the public 35-36 

cannot be isolated 110 

cause disease 36-37 

carriers, infective during incubation stage 34 

opsonic index in 35 

or mild cases, in Spanish War 38 

percentage of 34-35 

feces in yard 128, 131, 140 

fever among nurses 131-132 

and high temperature 365-366 

believed to be an intestinal disease 136 

by bathing 274-275 

contact 13, 37, 127-141 

in an almshouse 133 

hospitals 131-132 

the family 134 

civil life 129-131 

South Africa 129 

Spanish War 128-129 

on shipboard 134 

food infection. 127-128 

prosedemic infection 130 

decreases with removal of privies 139-141 

from bedbugs 351 

celery 319 

clothing 177 

crawfish 318 

dust 229-230 

flies ......; 127-129, 140-141 358-360 

flies, statistical evidence 363-365 

fomites 185 

handling typhoid cultures 133 

infected bedding 133 

milk 37, 288-289 

mud dumped near intake 270 

pail closets 139-140 

privies 127-128, 137-141 

rags 180 

sewer air 228-229 

shellfish 314-318 

soil infection ' 25 

soiled linen 177 

springs 274 

thermometer 132 

unrecognized cases 91 



INDEX 397 

Page 

Typhoid fever from water 267-275 

watercress 318-319 

wind blowing sewage to water works 270 

houses, infected flies in 352 

in barracks due to room infection 174 

mines 140 

Soldiers' home due to contact infection from 

physician 133 

Spanish War 13, 38 

Trier 13 

waitress due to contact infection 133 

infection stopped by strict cleanliness 132 

less with water closets 139-140 

not dust-borne . 239-240 

outbreaks continued by contact infection 130-131 

in Providence, R. I 14 

prevalent in country 131 

spread among patients by nurses 132 

by kitchen help 133 

by waitress 133 

"Typhoid Mary" 37 

Typhoid fever, an infection of the blood 30 

atypical 38-39 

causes of excess in cities 271 

contact outbreaks in cities t 130-131 

contracted by laundress from soiled linen 133 

death rate in Rhode Island 14 

filthy habits cause of 128, 131, 140 

mild cases in Panama 38-39 

Trier 39 

number of carriers 138 

Typhus fever not from clothing 174-175 

Typhus fever, not of extra-corporal origin 25 

Uncinaria, see Hookworms, Anchylostoma. 

Uncinaria americana 144 

due chiefly to contact 144-145 

Urine, bacillus typhi in 31 

cause of Mediterranean fever 18 

Vaccine, resistance to drying 201-202 

transport across ocean 200-202 

Vaginitis in Babies' Hospital 123-124 

Vegetables, amebae dysenteriae on 20 

Venereal diseases, see Gonorrhea ; Syphilis. 

Wage earners, isolation of 110, 120-121 

Waitress, typhoid fever spread by 133 

Warning sign in diphtheria 109 

Washing soiled linen in running streams cause of cholera 275 

Water and cholera 275-276 

diarrhea 277-278 

dysentery 276-277 



398 INDEX 

Page 

Water and malaria 278-279, 324 

tuberculosis 279-280 

typhoid fever 267-275 

worms 280 

yellow fever 279 

closets, typhoid fever less with 139-140 

outbreaks, characteristics 268-269 

supplies, infection of 14 

Water, bacillus typhi in 9, 269 

recovered from 269 

bacteria of suppuration in 21 

Water, filtration of 282 

infection by 266-283 

of milk by 273 

micrococcus, melitensis in 17 

mode of infection with typhoid bacilli 270 

municipal supplies infected 270, 276 

protection of 281-282 

purification of 282-283 

spirillum choleras in 15 

sterilization of municipal 283 

storage of 282 

Watercress, typhoid fever caused by 318-319 

Wells, amount of typhoid fever due to ... . 272-274 

cholera infection from 275-276 

conditions of safety 274 

infection from 266-267, 271-275 

protection of 281 

Whooping cough, not of extra-corporal origin 25 

Willard State Hospital, diphtheria in 102 

Wind blowing sewage to water works cause of typhoid fever 270 

Wool, anthrax from 185 

spores in 184-185 

Worms derived from water 280 

Wounds, infection of , by air 250-251 

Yellow fever an endemic disease 26 

and bagging 171 

ballast 171 

cloth 171 

fomites 171-172, 334 

fomites, experiments in Havana 203 

grain 171 

mattress 171 

merchandise 171 

mosquitoes 332-338 

oyster buckets 171 

quarantine 336 

mosquito destruction 337 

mosquito, habits of 335 

not due to soil infection 26 

from water 279 

virus filterable 333-334 



INDEX 399 

Page 

Yellow fever virus in blood 333-334 

Yellow fever, discovery of causation 332-334 

latent period in outbreaks 333-334 

mild and atypical cases 89 

preventive measures 336-337 

quarantine officers take the temperature of passen- 
gers for detection of 89 

screening of cases 336-337 

success of mosquito destruction 331, 335, 337-338 



AUG 13 1810 



